P2135 means the two throttle position sensor signals that should always agree have drifted apart, so the engine computer limits power for safety. Expect sudden reduced power, an EPC or wrench light, or “Reduced Engine Power”. A corroded connector or a worn sensor inside the throttle body is the usual cause; repairs typically cost $0-$800.
- P2135 is set when the two redundant throttle sensor signals, typically 0.5-4.5 V each, disagree beyond the allowed margin.
- Most repairs cost $0-$150 for a connector fix or $250-$800 for a new electronic throttle body.
- Sudden power loss in traffic is the main risk, so drive only short, careful trips until it is fixed.
- Cleaning the throttle body rarely fixes P2135; it is an electrical fault, not a carbon problem.
- What Does P2135 Mean?
- What Are the Symptoms of P2135?
- What Causes P2135?
- How Do You Diagnose P2135?
- How Do You Fix P2135 and What Does It Cost?
- Will Cleaning the Throttle Body Fix P2135?
- How Is P2135 Different From P2138 and P0122?
- Can I Drive With P2135?
- When Should You See a Mechanic?
- Is There a Recall or Extended Warranty for P2135?
- Frequently Asked Questions
- Related Guides
What Does P2135 Mean?
P2135 is the generic OBD-II code for “Throttle/Pedal Position Sensor/Switch A/B Voltage Correlation”. The engine computer reads two separate position signals that must always agree with each other. When signal A and signal B disagree by more than the allowed margin, it sets P2135 and limits engine power for safety.
Modern petrol engines use electronic throttle control (drive-by-wire): no cable, just a motor that opens the throttle plate. Because a wrong reading could make the car speed up unexpectedly, each position is measured twice, by two sensor tracks with different voltage curves, and the computer constantly checks one against the other.
On most vehicles “A” and “B” in P2135 are the two sensors inside the throttle body; some makes assign the letters differently, so check the service manual. The companion code P2138 covers the two accelerator pedal sensors (D/E).
| Sensor design | Throttle closed | Throttle wide open | How the two compare |
|---|---|---|---|
| Opposite slopes (common on GM) | Sensor 1 about 0.5-1 V, sensor 2 about 4-4.5 V | Sensor 1 about 4-4.5 V, sensor 2 about 0.5-1 V | The two add up to roughly 5 V at every position |
| Offset, same direction (common on Toyota) | Sensor 1 about 0.5-1.1 V, sensor 2 about 2-3 V | Both rise, sensor 2 stays higher | A fixed gap between the two lines |
These are typical values only; exact curves and the allowed mismatch vary by manufacturer and engine, so use the service manual figure for your vehicle.
What Are the Symptoms of P2135?
P2135 symptoms usually appear suddenly, because the engine computer reacts the moment the two signals disagree. The most common sign is a sharp loss of power with a warning light while driving, and a car that barely accelerates until it is restarted.
- Reduced power or limp mode: throttle opening is capped or fixed slightly open, sometimes limiting speed to about 20-40 mph. Our car stuck in limp mode guide explains this protective state.
- Brand-specific warnings: GM shows “Reduced Engine Power”, Volkswagen and Audi light the EPC light, and Ford lights an amber wrench lamp, with or without the check engine light.
- Poor or no response to the pedal, hesitation and a feeling that the car loses power when accelerating.
- Rough or high idle, cruise control disabled, occasionally stalling.
- An intermittent pattern: normal after a restart, then reduced power again over bumps or in wet weather.
What Causes P2135?
P2135 is caused by anything that makes one of the two position signals drift away from the other. Worn sensor tracks inside the throttle body and poor connections cause most cases; computer failures are rare. Check in roughly this order:
- Corroded or loose throttle body connector — corrosion, spread terminals or a half-latched connector changes one signal more than the other, especially on older vehicles.
- Worn throttle position sensor tracks — usually built into the throttle body. A worn spot near the cruising position causes a brief dropout, which is why the final fix is so often a throttle body.
- Chafed or broken wiring — harness rubbing on the engine, a bracket or the intake, especially where it flexes with engine movement.
- A 5-volt reference or ground problem — both sensors share a supply. A shorted sensor elsewhere on the same reference, or a poor ground, pulls the signals apart, usually with other sensor codes.
- Faulty accelerator pedal sensor — on makes that assign the A/B letters to the pedal.
- Low system voltage from a weak battery or charging fault.
- Engine computer fault — rare; only after the wiring and sensors are proven good.
How Do You Diagnose P2135?
Diagnosing P2135 takes about 45-90 minutes with a live-data scan tool and a digital multimeter; a graphing scan tool or oscilloscope makes it much easier. The aim is to find which signal drifts, and whether the sensor or the wiring is to blame.
With the ignition on, an electronic throttle can open and snap shut at any moment, including during self-tests and with the engine off. Never put fingers inside the throttle body unless the battery is disconnected.
1. Record all codes and freeze frame data (5 minutes)
P2135 with other sensor codes on the same 5 V reference points to a supply or ground fault. P2135 with P0122, P0123, P0222 or P0223 narrows it to one sensor circuit.
2. Check voltage, connector and harness (15 minutes)
Confirm about 12.4-12.7 V at rest and 13.5-14.5 V running. Then unplug the throttle body connector, look for corrosion, water and pushed-back pins, then reconnect firmly. With the key on and live data showing both throttle sensors, gently move the harness along its route. A jumping signal points to wiring, not the sensor.
3. Graph both sensors through the full sweep (15 minutes)
Key on, engine off, slowly press the accelerator to the floor and release it while graphing both throttle position signals. Both lines should move smoothly, keeping a constant relationship; a sudden dip at one point means a worn sensor track.
4. Test the 5 V reference and ground (15 minutes)
Back-probe the connector: reference about 4.8-5.2 V, ground under about 0.1 V to battery negative. A low reference with other codes suggests a shorted sensor sharing the circuit.
5. Check pedal sensor data (10 minutes)
Graph both accelerator pedal sensors the same way; glitching pedal signals point to the pedal assembly.
How Do You Fix P2135 and What Does It Cost?
Fixing P2135 means repairing whichever signal is drifting, and the most common final repair is a new electronic throttle body with built-in sensors. A connector repair is far cheaper, so prove the cause first. Typical US costs, October 2026 — varies by vehicle and region:
| Confirmed cause | Fix | Typical cost (parts + labour) |
|---|---|---|
| Corroded or loose connector | Clean terminals, apply dielectric grease, replace pigtail if damaged | $0-$150 |
| Chafed or broken harness | Locate and repair wiring, re-secure the harness | $100-$400 |
| Worn throttle position sensor | Replace electronic throttle body (separate sensor on a few designs) | $250-$800 |
| Faulty accelerator pedal sensor | Replace pedal assembly | $150-$450 |
| Shorted sensor on shared 5 V reference | Replace the shorting sensor | $100-$400 |
| Engine computer fault | Repair or replace and program | $500-$1,500 |
After a new throttle body, many vehicles need a throttle or idle relearn. Then clear the code and road test.
What doesn’t work: clearing the code without a repair, buying an engine computer before testing the wiring, and fitting a cheap unbranded throttle body whose sensor curves may not match.
Will Cleaning the Throttle Body Fix P2135?
Cleaning the throttle body rarely fixes P2135. Carbon on the throttle plate restricts idle airflow and causes idle codes such as P0507, but P2135 is an electrical disagreement between two sensor signals, which carbon does not change.
A cleaning can seem to help because reseating the connector disturbs corroded terminals for a while. Clean only if the throttle is visibly coated and idle is poor; follow our throttle body cleaning guide and keep cleaner away from the motor and sensor housing.
How Is P2135 Different From P2138 and P0122?
P2135, P2138 and P0122 all involve throttle control but describe different faults. P2135 and P2138 are correlation codes: two signals that should agree do not. P0122 is a single-circuit code: one throttle sensor voltage is below the possible range, which usually means a short or an open wire.
| Code | What the computer sees | Usual location |
|---|---|---|
| P2135 | Throttle position sensors A and B disagree | Throttle body sensor or its connector |
| P2138 | Pedal position sensors D and E disagree | Accelerator pedal assembly or its wiring |
| P0122 | Throttle sensor A voltage too low | Shorted or open sensor circuit |
When P2135 and P2138 appear together, check the shared supply, ground and battery voltage before replacing both assemblies.
Can I Drive With P2135?
You should not drive normally with P2135. The engine computer can cut power without warning, which is dangerous when merging, overtaking or crossing traffic. A short, careful drive to a repair shop on quiet roads is usually possible, but avoid motorways and heavy traffic, and have it diagnosed promptly.
When Should You See a Mechanic?
See a mechanic for P2135 when the car keeps dropping into reduced power, the graph test shows nothing, several sensor codes appear together, or the code returns after a new throttle body. More codes are in our trouble codes section.
Is There a Recall or Extended Warranty for P2135?
No general recall covers P2135, but some makers extended throttle body warranties. Ford’s Customer Satisfaction Program 13N03 gave 10 years or 150,000 miles on certain 2009-2013 Escape, Fusion, Milan and Mariner models for reduced power with the wrench lamp.
GM ran similar 10-year or 120,000-mile programs for some late-2000s models. Most have expired by age; a dealer can check by VIN.
Only a short, careful drive to a repair shop — power can cut out without warning, so avoid fast roads and heavy traffic.
Get the car checked promptly if it drops into reduced power more than once, P2135 appears with other sensor codes, or the code returns after a repair. Sudden power loss in traffic is a real crash risk, so avoid fast roads until it is fixed. Never put fingers in the throttle body with the ignition on — the electronic throttle can snap shut without warning.
Frequently Asked Questions
What is the most common fix for P2135?
The most common final fix for P2135 is a new electronic throttle body, because its built-in sensors wear. A corroded connector or chafed harness causes many cases too, so graph both signals and check the wiring first: a connector repair can cost under $150, a throttle body $250-$800.
Can a bad battery cause P2135?
Yes, sometimes. Low system voltage from a weak battery or charging fault can upset sensor signals and set correlation codes such as P2135, often with other voltage codes. Confirm about 12.4-12.7 V at rest and 13.5-14.5 V running before replacing throttle parts.
Why does P2135 come and go?
P2135 is often intermittent because the fault is a brief signal dropout from a worn sensor track or loose terminal. Bumps, engine movement, heat and moisture trigger it, so a car may drive normally after a restart and then fall back into reduced power.
Will disconnecting the battery clear P2135?
Disconnecting the battery usually clears P2135 and ends reduced-power mode, but it does not fix the cause. If the two signals still disagree, the code and power loss return, sometimes within minutes, and learned idle values are reset too.
Is P2135 the throttle position sensor or the pedal sensor?
On most vehicles P2135 refers to the two throttle position sensors in the throttle body, while P2138 covers the two accelerator pedal sensors. Some makes assign the letters differently, so confirm with the service manual or a manufacturer-level scan tool before buying parts.
Do I need to relearn the throttle after replacing it?
Many vehicles need a throttle or idle relearn after a new throttle body is fitted, either through a set key-on and idle procedure or a scan tool function. Skipping it can leave a high or unstable idle, even though P2135 itself is fixed.
