P2135 on Chevrolet: How to Diagnose & Fix
Throttle/Pedal Position Sensor Voltage Correlation
7 Chevrolet models · 7 documented issues · 5 critical · $100-$700 repair
P2135 on Chevrolet by model: symptoms, diagnosis and fix
The 2007-2013 Avalanche frequently enters "Reduced Engine Power" mode, severely limiting acceleration. The most common causes are the electronic throttle body wearing out or the accelerator pedal position sensor (APP sensor) developing faults. The vehicle becomes barely drivable in this mode, struggling to accelerate to highway speeds. The issue can occur intermittently before becoming permanent.
Common Symptoms
- "Engine Power Reduced" or "Reduced Engine Power" message on dash
- Vehicle struggles to accelerate past 20-30 mph
- Check engine light with P2128 or P2138 codes
- Intermittent power loss that resolves after restart
- Rough or hesitant throttle response
How to Fix
Diagnose with a scan tool to determine if the throttle body or accelerator pedal position sensor is the cause. Throttle body replacement costs $200-$400 parts and labor. APP sensor replacement costs $100-$250. A remanufactured throttle body from a quality source works well. Clear codes after repair and road test to verify.
What you need to diagnose it
The repair instructions explicitly call for reading stored codes. Use a scanner that can read the named code families before choosing a repair.The recommended scanner supports these code families; confirm your exact year, model and module coverage before buying.
ANCEL AD310 Classic OBD-II Scanner
Read & clear engine (P) codes
$20–$40View
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Reading and clearing the code is DIY work. Module replacement or reprogramming is not — most modules are VIN-programmed, so a new one does nothing until a shop codes it to your car. Check for an open recall or service bulletin before buying anything.
Sources for this issue (2)
The Cobalt is drive-by-wire: the pedal module houses two redundant APP sensors, and the PCM compares them against the electronic throttle body's two TPS signals. When one signal drifts out of correlation the PCM drops the car into Reduced Engine Power mode — throttle authority is cut to a fast idle with the wrench/RE POWER message on the cluster, often with no warning in traffic. Owners report it as an intermittent that starts as a stumble and progresses to repeated limp events. P2138 (APP sensor 1-2 correlation) is the dominant code. The real cause is split between a worn pedal module, a dirty or failing electronic throttle body, and — very commonly on this car — corroded or loose connector terminals, since water intrusion down the A-pillar from a clogged sunroof drain reaches wiring in this area.
Common Symptoms
- "Engine Power Reduced" message on the cluster
- Sudden loss of acceleration in traffic
- Wrench warning light
- Rough or surging idle
- Intermittent hesitation that clears after a restart
How to Fix
Read the code before buying parts. Back-probe and inspect the pedal connector and the throttle body connector for green corrosion, spread terminals, or a loose lock — a bad terminal mimics a failed sensor and is the cheapest fix. If the terminals are clean, scope or graph both APP signals while sweeping the pedal to see which one drops out. A carbon-fouled throttle body responds to cleaning plus an idle relearn; if the fault follows the pedal, replace the accelerator pedal module (often cheaper than the throttle body and the more common culprit). Perform the throttle-position relearn after any replacement.
Sources for this issue (4)
A widely reported Silverado 1500 complaint is a sudden cascade of dash messages — 'StabiliTrak disabled,' then 'Service StabiliTrak,' 'Service Traction Control,' and finally 'Engine Power Reduced' — sometimes with a stumble or stall and limited throttle response. The most common root causes are a faulty accelerator pedal position (APP) sensor or throttle body (electronic throttle), but GM bulletin 18-NA-161 also traces 'Service StabiliTrak' with engine stalling to high-resistance or loose battery cables, a poor BCM ground at G218 (behind the driver-side dash), a starter B+ cable shorting against the starter shield, or a weak battery. Because it can drop the truck into reduced-power limp mode at speed, owners treat it as urgent.
Common Symptoms
- 'Service StabiliTrak' and 'Service Traction Control' messages
- 'Engine Power Reduced' / limp mode
- Throttle becomes unresponsive or truck stalls
- Multiple ABS/traction/stability lights at once
- Symptoms come and go (intermittent)
How to Fix
Scan for stored codes (commonly P2138 and related APP/throttle codes) and read live throttle/pedal data. Start with the GM bulletin 18-NA-161 checks: voltage-drop test the battery cables and battery fuse block connections, inspect BCM ground G218 (trucks built before June 2015), check the starter B+ cable for contact with the starter shield, and test the battery. Then test/replace the APP sensor or throttle body as indicated. Apply any GM throttle-body or PCM software updates. Confirm the actual failed component before replacing the throttle body, as wiring/ground faults mimic sensor failure.
What you need to diagnose it
The repair instructions explicitly call for reading stored codes. Use a scanner that can read the named code families before choosing a repair.This issue involves C codes, which a basic engine-code reader cannot see.The recommended scanner supports these code families; confirm your exact year, model and module coverage before buying.
Autel MaxiCOM MK808S Diagnostic Tool
All-system diagnostics (25+ modules)
$350–$450View
As an Amazon Associate, we earn from qualifying purchases. Prices are approximate and may vary.
Reading and clearing the code is DIY work. Module replacement or reprogramming is not — most modules are VIN-programmed, so a new one does nothing until a shop codes it to your car. Check for an open recall or service bulletin before buying anything.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Accelerator pedal assembly with position (APP) sensor — 2014-2018 (K2XX generation)OEM23362231Cross-refDorman 699-213, A-Premium APP pedal (Amazon B0CFXK98R8, lists 2014-2018 Silv, GM 20972082 (superseded by 23362231)$86–$162
Only replace after confirming P2138/P2122-type codes are not caused by the door-sill body grounds or the underseat harness connector — c
- Electronic throttle body with sensor — 4.3L V6 (LV3), 2014-2021OEM12676296Cross-refGM 12632171 / 12671014 / 12669536 / 12648414 (all superseded, Standard Motor Products / Dorman aftermarket units sold as 2$100–$295
4.3L-only throttle body; do not use the V8 part. 2022 Silverado 1500 with 4.3L is not shown on the GMPartsGiant fitment (listed 2014-2021) — a 2022 4.3L owner should confirm by VIN.
- Electronic throttle body with sensor — 5.3L V8 (L83 / L84), 2014-2022OEM12713775Cross-refGM 12740725 (current supersession of 12713775), GM 12617792 (earlier 5.3L number cross-referenced by afterma, A-Premium / ADIGARAUTO aftermarket units listing OE 12617792$200–$359
Confirm the failed component with live TPS/APP data first; grounds and chafed underseat harness wiring are
- Electronic throttle body (87mm) — 6.2L V8 (L86 / L87), 2014-2021OEM12740727Cross-refGM 12678223 / 12729495 / 12733469 / 12620263 / 12713774 (all, GM 12678312 (2019-2021 6.2L listing on GMPartsGiant, itself $80–$200
6.2L uses the 87mm LT-family throttle body shared with Corvette/Camaro LT1 — not interchangeable with the 5.3L unit.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (2)
Impalas frequently throw a cluster of warnings at once — 'Engine Power Reduced,' 'Service StabiliTrak,' and 'Service Traction Control' — that are usually one underlying drive-by-wire fault rather than three separate failures. The most common root cause is the electronic throttle body actuator (or the dual throttle-position sensors inside it) going out of range; the accelerator pedal position sensors can also disagree. Because the ECM cross-checks these dual sensors, any disagreement forces the car into limp-home mode with drastically reduced power. Carbon buildup on the throttle plate aggravates it, especially in cold weather.
Common Symptoms
- 'Engine Power Reduced' message with limp-home mode
- 'Service StabiliTrak' and 'Service Traction Control' lights together
- Sudden loss of acceleration
- Rough or surging idle, worse in cold weather
- Intermittent recovery after key cycle
How to Fix
Scan for throttle/pedal DTCs before replacing parts. Start by cleaning the throttle body (a frequent cause, cheap fix). If codes/symptoms persist, replace the electronic throttle body assembly (ACDelco 12670981 fits the 2012-2013 3.6L; verify the correct unit for your engine/year). Some 3.6L applications require a relearn/idle relearn after replacement. If the pedal sensors are at fault, replace the accelerator pedal position sensor assembly.
Sources for this issue (2)
Tahoes with drive-by-wire throttle (APP pedal sensor + TAC module + electronic throttle body) commonly trigger a 'Reduced Engine Power' message and drop into limp mode with severely limited acceleration - a safety concern in traffic. On GMT800s the frequent culprits are a broken/chafed wire in the throttle-body harness (often the yellow wire), corroded engine grounds, or a dirty/sticking throttle body (P1516/P1515). GMT900s see similar throttle-actuator/APP faults (P2101/P2135/P0120 family).
Common Symptoms
- 'Reduced Engine Power' warning message
- Limp mode / severe loss of acceleration
- Hesitation or surging
- Check Engine light with throttle codes
- Intermittent power loss that clears on restart
How to Fix
Retrieve codes to isolate the branch: P1515/P1516 point at the TAC/throttle actuator, P2135/P0120-series at the TPS/APP correlation. Start with the cheap, common causes: clean the electronic throttle body, inspect and repair the throttle-body wiring harness (especially chafed/broken wires) and clean/tighten engine grounds. If the throttle body's internal TPS is faulty, replace the electronic throttle body assembly (ACDelco units available; part roughly $120-300). A failed APP pedal sensor is a less common cause.
Sources for this issue (1)
The GMT360 TrailBlazer uses a drive-by-wire throttle actuator control system with dual redundant sensors in both the throttle body and the accelerator pedal. When the two throttle position signals disagree the PCM sets P2135 and drops the truck into Reduced Engine Power limp mode — the vehicle will barely accelerate, which is dangerous when it happens pulling into traffic. Usual root causes are an internally failed electronic throttle body, a corroded or loose crimp in the throttle body connector, or moisture intrusion in the harness. Related codes P0641 (5V reference) and P1523 (throttle closed position performance) show up alongside it.
Common Symptoms
- 'Reduced Engine Power' message on the dash
- Vehicle will barely accelerate / limp mode
- Check engine light with P2135
- Rough or hunting idle
- Intermittent stall or no throttle response
How to Fix
Do not simply throw a throttle body at it. Inspect the throttle body connector terminals for a loose crimp between the terminal and the copper strands and for green corrosion — a widely reported fix on this platform. Clean carbon from the throttle bore, since heavy buildup causes P1523. If the two TPS signals still fail to track on a scan tool, replace the electronic throttle body assembly (roughly $150-400 for the part) and relearn idle. If pedal position codes appear instead, the accelerator pedal position sensor assembly is the culprit. No recall covers this.
Sources for this issue (3)
P2135 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P2135 mean on a Chevrolet?
P2135 stands for "Throttle/Pedal Position Sensor Voltage Correlation." P2135 means the powertrain computer detected that the two throttle position (TP) or accelerator pedal position sensors disagree with each other. Drive-by-wire systems use redundant sensors so the PCM can cross-check the throttle or pedal reading for safety; if the two signals don't correlate within an expected range, this code sets. As a fail-safe, the vehicle often enters a reduced-power 'limp' mode, causing sluggish acceleration, a stuck or hesitant throttle, and a warning light. Because it affects throttle control, it should be addressed promptly. On Chevrolet it is documented across 7 models: Avalanche, Cobalt, Silverado 1500, Impala, Tahoe, TrailBlazer, Suburban.
What are the most common causes of P2135?
The most common causes of P2135 are: Faulty throttle position sensor / throttle body assembly, Faulty accelerator pedal position sensor, Damaged wiring or connectors at the throttle body or pedal, Corroded or loose connector terminals, Poor ground or reference voltage problem, Carbon buildup binding the electronic throttle plate, Failed PCM (rare). The specific cause varies by vehicle.
How much does it cost to fix P2135 on a Chevrolet?
Published repair estimates on Chevrolet range from $100 to $700 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.