P2135 Code: Throttle Position Sensor A/B Voltage Correlation
The two position signals inside the throttle body disagree, so the PCM can no longer trust throttle angle.
At a glance
Severity: Moderate
- Meaning
- Throttle Position Sensor A/B Voltage Correlation
- System
- Speed & Idle Control · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $50–$900
- DIY difficulty
- Moderate
An electronic throttle body carries two position sensors on the same shaft, and the PCM checks them against each other many times per second. On the common mirror-image design, sensor A climbs from roughly 0.5–1.0 V at closed throttle to above 4 V wide open while sensor B falls from about 4.0–4.5 V to under 1 V, so the pair always adds up to close to 5 volts. Other designs run both signals upward with a fixed gap; many Toyota units, for example, show about 0.5–1.1 V on the first sensor and 2.1–3.1 V on the second at closed throttle. When the two drift apart by more than a few percent of travel, P2135 sets and the PCM cuts power to the throttle motor. The most frequent cause is a worn resistive track inside the throttle body at the angles the engine uses most, ahead of corroded or loose terminals in the throttle body connector.
Can I keep driving? Expect a fixed fast idle and almost no power. Drive only a short distance at low speed to get safely off the road or to a shop, and be ready for the power to cut out again without warning.
How to read P2135
- P Powertrain
- 2 Generic (SAE)
- 1 Fuel & air metering
- 35 Specific fault
Symptoms
- Check engine light with a Reduced Engine Power or similar warning
- Throttle parked at a fixed opening: raised idle and hardly any response to the pedal
- Sudden power loss at part throttle that comes back after an engine restart
- Stumble or surge that always happens at the same pedal position, often light cruise
- Fault returns after an engine bay wash or driving through heavy rain
- TP sensor A and B percentages in live data that separate instead of moving together
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Worn resistive track in a contact-type throttle position sensor, usually at idle or light-cruise angles
- Corroded, spread or loose terminals in the throttle body connector
- Harness chafed or cracked near the throttle body where the engine rocks on its mounts
- Water or spray cleaner that got into the sensor housing
- 5-volt reference or sensor ground problem that shifts one signal more than the other
- Incorrect replacement throttle body or PCM input fault
Diagnosis step by step
Check freeze frame and add the two voltages
Note the throttle percentage and rpm stored when the code set; it tells you which part of the track is suspect. Key on, engine off, read TP A and TP B in volts. On mirror-image designs they should total about 5.0 V at any angle; on offset designs the gap should stay constant.
Tools: OBD-II scanner
Graph both sensors during a slow sweep
On most drive-by-wire cars the pedal moves the throttle with the key on and engine off. Press the pedal slowly to the floor and back over about ten seconds while graphing both signals. A spike, dropout or flat spot on one trace at the same angle every time points to a worn track.
Tools: OBD-II scanner
Wiggle the connector and harness
Keep the graph running and flex the throttle body connector and the first foot of harness. A glitch that follows your hand is a wiring or terminal problem, not wear. Unplug the connector and look for green corrosion, spread female terminals and moisture.
Tools: OBD-II scanner, Flashlight
Verify reference and ground at the throttle body
Back-probe the connector with the key on. The reference should read 4.9–5.1 V and the sensor ground should sit within about 0.1 V of battery negative. A poor ground raises both signals and can break the sum or offset relationship even with a healthy sensor.
Tools: Multimeter
Decide between sensor and throttle body
On most modern throttle bodies the position sensors are built in and not sold separately, so a worn track means a new throttle body. Only some older designs have a bolt-on sensor. Cleaning carbon off the plate does nothing for a worn track.
Tools: Screwdriver
Replace, relearn and repeat the sweep
After the repair, clear the codes and run the throttle relearn your vehicle needs, often just a key-on wait or a scan tool routine. Repeat the graphed sweep to confirm both traces are smooth and track each other across full travel.
Tools: OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean, tighten or repin throttle body connector | Yes | $50–$180 |
| Repair harness to the throttle body | No | $120–$350 |
| Replace electronic throttle body with integrated sensors | Yes | $300–$900 |
| Replace separate throttle position sensor (older designs) | Yes | $110–$300 |
| Throttle relearn with a scan tool at a shop | No | $60–$150 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Chevrolet
On many GM cars and trucks with electronic throttle, P2135 comes with a Reduced Engine Power message. Throttle body replacement or repair of the throttle body connector terminals is the usual fix; check the connector before buying the part.
Field data
| Chevrolet | 56 | ||
|---|---|---|---|
| Ford | 14 | Focus, Transit Connect, Escape | |
| Hyundai | 8 | Sonata, Santa Fe, Veracruz | |
| Kia | 6 | ||
| GMC | 5 | Envoy Xl, Sierra 1500 Hybrid, Terrain | |
| Jeep | 3 | Patriot, Compass | |
| Nissan | 3 | Altima Hybrid, Sentra, Versa Note | |
| Honda | 2 | Accord, Pilot |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
P2135 turns on the check engine light, which fails an OBD-II emissions inspection. After the repair, drive normally until the readiness monitors are complete before retesting.
Frequently asked questions
Why does a disagreement between two sensors put the car in limp mode?
The PCM has no way to tell which of the two signals is correct, and a wrong throttle angle could mean unwanted acceleration. It therefore switches off the throttle motor and lets springs hold the plate at a safe fixed opening.
Will cleaning the throttle body fix P2135?
Rarely. Carbon on the plate affects airflow, not the position signals. A worn track inside the sensor stays worn, and solvent sprayed into the sensor area can make things worse.
Can I replace just the throttle position sensor?
Only on designs where it's a separate bolt-on part. Most electronic throttle bodies have the sensors sealed inside the housing, so the whole throttle body is the replacement part.
I have P2135 and P2138 together. Is that two bad parts?
Usually not. When the throttle and pedal sensors both report correlation faults, look first at something they share, such as a 5-volt reference, a sensor ground splice or the PCM's ground connections.