Skip to content
CarTipsMentor

Reduced Engine Power Warning: Causes & Fixes

What GM's Reduced Engine Power message means, the throttle, sensor and wiring faults behind it, how far you can drive, what to do right away, which GM bulletins apply and what the repairs cost.

Digital instrument cluster with the amber check engine, parking brake and battery lights lit
Written by
CarTipsMentor Team
OBD2 Codes guides
Published
Updated
Reading time
18 min

Key takeaways

Reduced Engine Power means the engine computer found a fault it can't trust, most often in the electronic throttle body, the throttle or pedal position sensors or their wiring, and cut power on purpose to protect the engine. Drive only a short, gentle distance away from fast traffic, then have the codes read before anyone clears them.

  1. 01On some throttle and pedal sensor codes, RepairPal says the computer may hold the car to 20 mph or less, so get out of fast traffic as soon as it's safe.
  2. 02A restart often brings power back for a while, but the fault and its stored codes are still there.
  3. 03GM's bulletins on code P2135 tell technicians to clean the throttle and fit a new sensor cover before replacing the whole throttle body.
  4. 04RepairPal puts a throttle body replacement at $623 to $766 and a throttle position sensor at $185 to $258.

This guide belongs to our OBD2 guide: dashboard warning lights section, which covers the wider topic.

Reduced Engine Power is the message General Motors uses on Chevrolet, GMC, Buick and Cadillac models when the engine computer finds a fault and deliberately limits power. CarParts.com's reduced engine power guide calls it a fail-safe, or limp, mode that every modern car has in some form, and notes that Ford vehicles can show the message for much the same reason.

The usual cause sits in the electronic throttle system: the throttle body, its position sensors, the gas pedal sensor or the wiring between them. You can usually creep a short distance at low speed, but treat the message as urgent.

It's one of many warnings a modern car can show, and our dashboard warning lights explained section explains what the other lamps and messages on your dash mean.

Reduced Engine Power at a Glance

What else is happening when the message appears tells you how urgent it is.

Reduced Engine Power at a Glance: table
What you seeWhat it usually meansWhat to do
Message on, car still drives normallyA fault is stored and power may drop on a later driveHave the codes read soon
Message on, car sluggish or stuck at low speedLimp mode is activeLeave fast traffic, drive gently or tow
Message with a flashing check engine lightA serious engine problemStop and call for roadside help
Message with a temperature or oil warningOverheating or low oil pressureStop and shut the engine off
Message after throttle body or battery workThe idle position was not relearnedHave a throttle or idle relearn done

Based on CarParts.com, RepairPal, Cars.com, Christian Brothers Automotive and General Motors service bulletins.

What Does Reduced Engine Power Mean?

It means the engine computer has switched to a protective mode that limits throttle opening, engine speed or both until the fault is repaired.

With electronic throttle control, no cable links the gas pedal to the engine. CarParts.com says GM's throttle actuator control system, first used on the 1997 C5 Corvette, reads two accelerator pedal position (APP) sensors to judge how much power you want. It checks a pair of throttle position (TP) sensors and drives a small motor that opens and closes the throttle plate.

The sensors come in pairs so the computer can cross-check them. GM bulletin 12-06-04-003A says code P2135 sets when the difference between TP sensor 1 and TP sensor 2 exceeds a calibrated value for more than 2 seconds, and pairs it with the check engine light and the Reduced Engine Power message.

RepairPal's P2119 code page says limp home mode limits engine power to prevent unwanted acceleration. CarParts.com adds that the limit may not start right away, and that in some cases the computer cuts fuel and the car can't be driven at all.

How much power you keep in limp mode

It depends on the fault and the carmaker, from a crawl to a slow cruise.

What Does Reduced Engine Power Mean?: table
SourceVehicles or codesWhat the reduced mode allowed
RepairPalThrottle and pedal sensor codes such as P2135Speed limited to 20 mph or less
Kelley Blue BookLimp mode in generalAbout 2,000 to 3,000 rpm and around 35 mph
NHTSA2009 to 2013 Ford Escape, Fusion, Mariner, MilanMost often held near 900 rpm; other modes kept speed above 20 mph
General MotorsChevrolet Volt and Cadillac ELRMessage shows when the battery reports less than 35 kW available

From RepairPal's P2135 code page, Kelley Blue Book's limp mode guide, NHTSA investigation PE13-003 and GM bulletin PIP4869E.

Kelley Blue Book's limp mode guide adds that an automatic may stay in second or third gear and the air conditioning may shut off.

What Other Carmakers Call It

The wording varies by carmaker, and even GM uses three versions on its gas models.

What Other Carmakers Call It: table
Make or vehicleWhat you may see
Chevrolet, GMC, Buick, CadillacReduced Engine Power, Engine Power is Reduced or Engine Reduced Power
Chevrolet Volt and Cadillac ELRPropulsion Power is Reduced
ChevroletA Propulsion Power Limited light
Ford and Mercury (Escape, Fusion, Mariner, Milan)Check engine or wrench light, with a limp-home mode Ford calls FMEM
Ram diesel pickupsExhaust Filter Full, Power Reduced See Dealer
Most modern vehiclesLimp mode or limp home mode, and turtle mode on many EVs

From GM service bulletins, Chevrolet's warning light guide, NHTSA investigation PE13-003, the 2022 Ram 2500/3500 owner's manual and Kelley Blue Book.

Chevrolet's warning light guide says its Propulsion Power Limited light comes on when the vehicle detects a propulsion system fault. You can still drive, but maximum acceleration and speed may be limited.

The plug-in hybrid version is often normal. GM bulletin PIP4869E says the 2011 to 2015 Volt and 2014 to 2016 ELR show it on severe mountain grades and at startup when the battery is at or below 5°F, and need a dealer only if the check engine light comes on too.

NHTSA's closing report on Ford throttle bodies counted 11,960 reports of throttle body malfunctions on about 1.59 million 2009 to 2013 Escape, Mariner, Fusion and Milan models with 2.5L and 3.0L engines, most of them involving reduced power in limp-home mode. Ford extended throttle body coverage to 10 years or 150,000 miles from the warranty start date under Customer Satisfaction Program 13N03.

For diesels, the 2022 Ram 2500/3500 owner's manual says a full exhaust filter makes the engine computer derate the engine to limit the likelihood of permanent damage to the aftertreatment system.

Signs That Come With the Warning

Most drivers feel it before they read it: the gas pedal goes soft and the car won't build speed.

  • Weak acceleration, especially on the highway, according to Christian Brothers Automotive's reduced power guide
  • Trouble holding a steady speed, or an erratic idle
  • Worse fuel economy as the engine struggles to keep its power
  • A check engine light before or with the message
Tachometer below 1,000 rpm with the car in Drive and the amber tire pressure light lit

Not every power cut is a fault. Kia's stability control manual page says engine power may decrease while electronic stability control is working, and pressing the gas on a slippery surface may not raise engine speed.

If a traction or stability lamp comes on too, our guide to the traction control light explains what each version of that lamp means.

What Causes Reduced Engine Power? Most Likely First

Start with the electronic throttle system. CarParts.com lists the throttle body first, then the pedal and throttle sensors and their circuits, and most of GM's bulletins on the message point there too.

A dirty or failing electronic throttle body

Firestone's reduced engine power guide names carbon buildup, faulty throttle position sensors, wiring issues and electronic throttle failures as the usual throttle body problems.

RepairPal warns that the throttle position sensor is often blamed for throttle body issues, and says to confirm the accelerator pedal isn't the real culprit before replacing an electronic throttle body.

A worn accelerator pedal position sensor

The pedal sensor is usually built into the gas pedal assembly. RepairPal's P2122 code page says the computer sets that code when the APP sensor signal doesn't change properly as you press or release the pedal.

YourMechanic's pedal sensor estimate notes the sensor can't be checked visually and can work intermittently, causing lagging or no acceleration and no throttle response in Park or Neutral.

Damaged wiring, connectors and grounds

CarParts.com lists damaged wires or poor connections anywhere in the throttle control circuit, and Kelley Blue Book says a loose connection can block the signal entirely. GM's P2135 bulletins have technicians check the throttle motor terminals when the old sensor cover comes off and discard any left stuck to the motor.

A skipped idle relearn after service

Electronic throttles need to learn their closed position. RepairPal's P2176 code page says an idle relearn may be required any time the battery is disconnected or the throttle body is serviced or replaced, and if it isn't done, the computer may limit power.

CarParts.com says many GM vehicles need an idle relearn whenever the throttle body is cleaned or replaced, citing GM bulletin PIP4578B, and GM's P2135 and P16A1 bulletins both include a throttle or idle learn.

A dirty mass airflow sensor or an air leak

AutoZone's reduced engine power guide says bad readings from the mass airflow (MAF), throttle position or oxygen sensors make the engine computer pull back output. It suggests trying MAF cleaner before replacing the sensor and checking for cracked vacuum hoses.

Air that sneaks in after the MAF sensor makes the engine run lean. Our P0171 code guide shows how to find vacuum leaks and test the MAF sensor with a scanner.

Misfires and weak fuel delivery

AutoZone lists worn spark plugs, bad ignition coils and damaged plug wires, and says hesitation under acceleration points to ignition. Innova's DIY guide to reduced power suggests listening for the fuel pump when the key is turned to On, since silence may mean a faulty pump.

If your scanner shows misfire codes, our P0300 code guide covers spark plugs, coils and injectors in order.

A clogged catalytic converter or transmission fault

AutoZone says a blocked converter creates back pressure, with a possible sulfur smell and flat performance under hard acceleration. The transmission computer can trigger limp mode too: AutoZone's limp mode explainer lists transmission overheating, low fluid and faulty sensors, and Kelley Blue Book adds a bad transmission solenoid.

Turbo, boost and diesel faults

RepairPal's P0299 code page says the engine computer sets that underboost code when the turbo or supercharger isn't providing the boost it requested. For Duramax diesels, CarParts.com points to bulletins on a damaged MAP sensor connector or an air intake leak.

GM bulletin PIE0289A covers intermittent reduced engine power with no trouble codes on 2011 to 2014 Chevrolet Cruze and 2012 to 2014 Sonic models with the 1.4L turbo.

Low battery voltage or a weak alternator

Here the sources disagree. CarParts.com lists a failing alternator and a nearly drained battery, while Kelley Blue Book says a faulty battery generally doesn't activate limp mode.

Low voltage can set its own code. RepairPal's P0562 code page says that code sets when battery voltage drops below 10 volts, and rates it Urgent.

Overheating, low oil and software

Kelley Blue Book lists overheating and low coolant, oil or transmission fluid as triggers, and Christian Brothers Automotive says the engine computer itself may need a software update.

GM bulletin PI1459 covers 2015 GM trucks, SUVs and the Corvette Z06 with 6.2L engines that showed Engine Power is Reduced within 30 seconds of a cold start, and GM's fix is a software update.

GM Bulletins and Special Coverage for Reduced Engine Power

GM has published several bulletins on this message, and the pattern is clear: clean and repair the throttle body before replacing it.

GM Bulletins and Special Coverage for Reduced Engine Power: table
BulletinVehiclesCodeGM's fix
12-06-04-003A2006 to 2011 GM cars, vans and SUVs including Impala, Malibu, Equinox, G6 and VueP2135Clean the throttle, new TP sensor cover, throttle body only if sensors still disagree
11-06-04-007C2008 to 2011 GM trucks, vans and SUVs including Silverado, Sierra, Tahoe and YukonP2135Clean the throttle, new TP sensor cover, engine computer update
Special Coverage 145822008 to 2012 GM models including Malibu, Impala, Traverse, Acadia, Enclave and CTSP2135, P0121 or P0221New throttle body or a TP sensor cover kit
132542014 Silverado and Sierra with the 5.3L V8P16A1New throttle body and idle learn
PIE0289A2011 to 2014 Cruze and 2012 to 2014 Sonic, 1.4L turboNoneRecord the power-loss history, then contact GM
PI14592015 GM trucks, SUVs and Corvette Z06 with 6.2L enginesP16F3Engine computer software update

From GM service bulletins and special coverage documents published on NHTSA's website. Ask a GM dealer to check your VIN for bulletins that apply.

GM bulletin 11-06-04-007C tells technicians not to replace the throttle body at first, and to replace it only if the TP sensors still disagree or codes P1516, P2101 or P2176 set after the new cover goes on.

GM Special Coverage 14582 says the TP sensor may make the engine run rough, turn on a reduced power message and reduce engine power. It covered the condition for 10 years or 120,000 miles from the date the vehicle was first placed in service, whichever came first.

The September 2015 document sets no calendar end date, but with the newest covered vehicles now 2012 models, that 10-year window has closed for nearly all of them.

GM's warranty labor times help you judge a quote: 1.2 hours to diagnose, clean the throttle and fit the TP sensor cover in bulletin 12-06-04-003A, and 0.4 hours for the throttle body and idle learn in GM bulletin 13254. An independent shop's book time may differ.

Is It Safe to Drive With Reduced Engine Power?

Only for a short, gentle trip off busy roads to a safe spot or a nearby shop. Don't drive on if the check engine light flashes or a temperature or oil warning comes on.

Kelley Blue Book says that for a minor cause, driving five miles to a shop or home likely won't do damage, but its general advice is to pull over and turn off the engine. CarParts.com recommends a tow, because more driving could cause more damage and the car may shut off completely.

Traffic is the bigger danger. Cars.com's limp mode guide warns that going slowly in fast-moving traffic is dangerous.

NHTSA's Ford investigation centered on throttle failures that caused a sudden reduction of engine power, and RepairPal's P2135 code page rates that code Urgent, meaning immediate action is necessary.

Get out of fast traffic first

In limp mode the car may not get past 20 to 35 mph. Turn on your hazard lights, move right and leave the highway at the first safe exit, and don't try to merge or pass.

What to Do When the Warning Comes On

Work through these steps in order.

  1. Ease off and get out of traffic. Turn on your hazard lights, move to the right and stop somewhere safe.
  2. Check the other lights and gauges. Christian Brothers Automotive says to call roadside assistance if the check engine light is flashing, and our guide to the steady vs flashing check engine light explains why. A temperature or oil warning means shut the engine off.
  3. Shut the engine off, wait and restart. Christian Brothers Automotive suggests 15 to 20 seconds and Kelley Blue Book at least 60, so wait a full minute.
  4. Check the oil and coolant. Cars.com says to wait a couple of minutes for the oil to drain back into the pan before reading the dipstick, and not to open the radiator cap while the radiator is hot.
  5. Drive gently and briefly, or tow. Firestone advises avoiding long trips and heavy towing until the car is inspected.
  6. Get the codes read before anyone clears them. AutoZone's Fix Finder service reads codes free, and GM's Cruze bulletin has technicians record the Reduced Engine Power History before clearing codes.
  7. Note when it happened. AutoZone suggests noting whether the power loss came under hard acceleration, at idle or after warmup.

Does Restarting Clear the Warning?

Often, but only for a while. A restart reboots the computer and may bring back full power, but the fault is still there.

Cars.com says cars rarely fix themselves and a mechanic may still find stored codes. Kelley Blue Book warns limp mode may return once the engine heats up again. CarParts.com says the warning goes away once the car is fixed and the codes are cleared.

How to Diagnose Reduced Engine Power With a Scan Tool

Read the stored codes first, then use live data to see which sensor or circuit the computer stopped trusting.

  1. Read every code, current and history, since GM notes P2135 can be stored either way.
  2. Save the freeze frame data before you clear anything.
  3. Watch the throttle and pedal sensors in live data. GM's bulletins have technicians check a parameter showing whether TP sensors 1 and 2 agree, and it should read Agree.
  4. Look up bulletins for your model. CarParts.com suggests a repair database such as ALLDATA DIY or Mitchell DIY.
  5. Inspect the connectors at the throttle body and gas pedal for corrosion, loose pins and chafed wires.
  6. Repair, relearn and test drive. Do the throttle relearn after any throttle body work, then clear the codes and confirm they stay gone.

A basic code reader reads and clears codes, but live sensor data usually takes a scan tool. Our roundup of the best OBD2 scanners explains the difference between a code reader, a scan tool and a bidirectional tool.

Codes that often come with the warning

How to Diagnose Reduced Engine Power With a Scan Tool: table
CodeMeaningRepairPal severity
P2135Throttle/Pedal Position Sensor/Switch A/B Voltage CorrelationUrgent
P2138Throttle/Pedal Position Sensor/Switch D/E Voltage CorrelationUrgent
P0121Throttle/Pedal Position Sensor/Switch A CircuitUrgent
P2122Throttle/Pedal Position Sensor/Switch D Circuit LowUrgent
P2101Throttle Actuator A Control Motor Circuit Range/PerformanceUrgent
P2119Throttle Actuator Control Throttle Body Range/PerformanceUrgent
P2176Throttle Actuator Control System, Idle Position Not LearnedUrgent
P0299Turbocharger/Supercharger A Underboost ConditionModerate
P0562System Voltage LowUrgent

Definitions and severity ratings from RepairPal's code pages. GM codes such as P1516, P16A1 and P16F3 appear in GM bulletins without definitions, so check your make's service information.

RepairPal also warns that just replacing a sensor may not fix the underlying issue, which is why GM's bulletins recheck sensor agreement after the repair.

What Reduced Engine Power Repairs Cost

Throttle and sensor repairs run from $185 to $766 in RepairPal's averages, while a charging or transmission fault can cost far more.

What Reduced Engine Power Repairs Cost: table
RepairTypical costSource and notes
Throttle position sensor$185 to $258RepairPal, labor $78 to $114
Accelerator pedal position sensor, Chevrolet Malibu$223YourMechanic, $128 parts and $95 labor
Accelerator pedal position sensor, Nissan Rogue$412YourMechanic, $317 parts and $95 labor
Mass airflow sensor$274 to $381RepairPal, labor $51 to $75
Throttle body replacement$623 to $766RepairPal, parts $492 to $573
Alternator replacement$809 to $1,088RepairPal, labor $196 to $288
Transmission rebuild or replacement$2,500 and upAutoZone

RepairPal averages last updated September 3, 2026, before taxes and fees. YourMechanic figures are model averages. Transmission figure from AutoZone's limp mode explainer.

The throttle body is the big-ticket part. RepairPal's throttle body estimate says a technician may recommend cleaning the throttle body or reprogramming the engine computer before replacing it, the same order GM's bulletins follow.

A sensor is cheaper, but only if it's the right one. RepairPal's throttle position sensor estimate says the part is often misdiagnosed on a hunch and recommends high-quality OEM sensors.

YourMechanic's Malibu pedal sensor estimate averages $223, but its model-year table runs from $355.95 for a 2015 2.5L to $596.29 for a 2016 1.5L turbo.

To check a quote against these figures, plug its numbers into our repair cost estimator, which turns the parts, labor hours and shop rate into a total.

Free tool

Repair Cost Estimator. Enter the parts price, labor hours, shop rate and diagnostic fee from your throttle body or sensor quote to see the total, the parts-only DIY cost and the labor you'd save. For a MAF quote, its comparison menu lists CarMD's $346 national average for a mass air flow sensor.

Can You Prevent Reduced Engine Power?

Partly. Routine care removes some triggers, but no schedule stops a sensor or throttle motor from wearing out.

  • Follow the factory maintenance schedule. AutoZone also suggests the correct oil viscosity, cleaning the MAF sensor every 20,000 to 30,000 miles and checking vacuum lines at oil changes.
  • Use the fuel and oil your manual calls for. Innova lists quality fuel and oils among its prevention tips.
  • Don't put off a check engine light. Innova lists prompt attention to check engine light problems as a prevention tip.

When to See a Mechanic

Book a diagnosis soon if any of these apply:

  • The message comes back after a restart or whenever the engine warms up.
  • It came with a flashing check engine light, an overheating gauge or an oil warning.
  • The codes point to the catalytic converter or transmission, which AutoZone says need professional equipment.
  • There are no codes at all, as GM's Cruze and Sonic bulletin describes.
  • You replaced a part and the message returned.

Reduced Engine Power is the car protecting itself. Get out of traffic, read the codes before they're cleared, check for a bulletin on your model and clean or test the throttle before paying for a new one.

Frequently Asked Questions

Can low oil cause reduced engine power?

Yes, on some vehicles. Firestone says low oil, oil leaks or poor oil pressure can trigger reduced power mode, and CarParts.com says low engine oil or coolant may trigger the warning. Cars.com warns that low oil pressure can destroy an engine in fairly short order, so stop, switch the engine off, wait a couple of minutes and check the dipstick before driving any farther.

Can a dirty air filter cause reduced engine power?

It can reduce power. AutoZone says a dirty air filter starves the engine of air, and Innova says a clogged filter can upset the air-fuel mixture. AutoZone suggests holding the filter up to a light and replacing it if you can't see through it. Kelley Blue Book also lists inspecting the engine air filter as a basic step when a car goes into limp mode.

Can the wrong fuel cause reduced engine power?

It can. AutoZone advises using the fuel grade your owner's manual specifies, because lower octane than the engine needs can cause knock and lost power. Innova adds poor-quality or contaminated fuel to its list of fuel delivery causes. If the warning appeared right after a fill-up, mention the station and grade to the technician reading your codes.

Will disconnecting the battery reset reduced engine power?

It may clear the message for a while, but Firestone says it won't fix the cause. It can also create a new problem: RepairPal says an idle relearn may be needed after the battery is disconnected, and skipping it can set code P2176 and limit power again. Have the codes read before you touch the battery.

Why does the reduced engine power warning come and go?

An intermittent fault is the usual reason. YourMechanic notes that an accelerator pedal sensor can work intermittently, and Kelley Blue Book says limp mode may return once the engine heats up. GM even issued a bulletin on intermittent reduced engine power with no trouble codes on 1.4L turbo Cruze and Sonic models, asking technicians to record the car's data before clearing anything.

Can I replace a throttle body or sensor myself?

Often, if the diagnosis is right. RepairPal says replacing a throttle position sensor usually needs only a screwdriver, but the part is often misdiagnosed. After throttle body work the idle position must be relearned, and GM's P2135 bulletins end with a throttle learn reset. Without that step, RepairPal says code P2176 can set and bring the warning back.

Sources and References

Written by

CarTipsMentor Team

Researched from the sources listed above and checked against them before publishing. Nobody paid to be mentioned on this page. It is general information, not advice about your own vehicle.

Published . Last updated .

Who writes for usEditorial policyDisclaimer

All guides