P2135 and P2138: throttle and pedal sensor correlation faults

Drive-by-wire systems are built on redundancy. Two sensors at the pedal, two at the throttle, all four cross-checked continuously. When a pair disagrees, the system does not try to guess which one is right — it limits power and sets a code.

Code	Meaning
P2135	Throttle position sensor A/B correlation
P2138	Pedal position sensor D/E correlation

That distinction is the whole value of these codes.

• P2135 → the fault is at the throttle body.
• P2138 → the fault is at the pedal.

Related: P0121 to P0123 throttle position sensor and P2122 and P2123 pedal sensor D.

Why the two sensors have different slopes

By design, so a fault cannot hide.

If both sensors in a pair rose identically from 0.5 V to 4.5 V, a short between the two wires would produce two identical readings — which looks perfectly healthy.

Giving them different ranges means identical readings are impossible in normal operation. Two matching values are proof of a short, not proof of health.

That is exactly what P2135 and P2138 detect.

P2138: the pedal

The pedal is used thousands of times per journey, mostly over the first third of its travel. Potentiometric tracks wear there first, and one track wears faster than the other.

Causes:

• Worn track, producing a dropout at a specific angle.
• Connector problems in the footwell.
• Water, from a blocked scuttle drain or a leaking door seal: damp carpet and electrical faults.
• A shorted harness, which produces the matching-values case.
• Aftermarket pedal boxes wired into this circuit.

The good news: the pedal assembly is inside the cabin and usually replaceable in under an hour.

P2135: the throttle body

Causes:

• Carbon preventing the plate reaching its expected position: P2119 throttle body range/performance.
• Worn sensor tracks inside the throttle body.
• Connector or wiring on a hot, vibrating component.
• Adaptation not relearned after cleaning or replacement: P2176 throttle idle position not learned.

The test that shows it

Log all four values together — both pedal sensors and both throttle sensors — then sweep the pedal slowly from rest to full and back.

Observation	Meaning
Four smooth traces, two distinct slopes each end	Healthy
Two pedal traces diverge at one angle	Worn pedal track — P2138
Two pedal traces identical	Shorted together
Throttle traces diverge	Throttle body — P2135
Throttle lags pedal, both pairs consistent	Binding rather than sensors

Sweep slowly. The whole point is to catch a narrow angle where one track drops out, and speed hides it.

Reading live data graphs properly.

What you will experience

• Sudden power limitation, engine capped at low RPM: limp mode.
• A dead spot in the pedal travel.
• Hesitation, or a jerk when reapplying throttle: car jerks when accelerating.
• Cruise control unavailable.
• Intermittent recovery after a restart.

That last behaviour is characteristic. The system re-checks at each start, finds agreement momentarily, and cuts power again once the worn angle is crossed.

P2110 alongside

Very common, and not an additional fault. P2110 means “forced limited RPM” — the announcement that power has been capped.

Fix the correlation code and P2110 goes with it: P2101 and P2110 throttle actuator control.

Why not to bypass it

You will find suggestions online for defeating these checks. The redundancy exists because an unintended throttle opening is dangerous, and the cross-check is what makes an electronic throttle acceptable at all.

A car that cuts power when its sensors disagree is behaving correctly. The repair is to make them agree.

Step by step

1. Read the exact code — it names the end of the system.
2. Log all four sensor values through a slow sweep.
3. Identify which pair diverges, and at what angle.
4. Check the connector at that end.
5. Check for water in the footwell for pedal faults.
6. Replace the assembly, then perform any required adaptation.

You can check this yourself. Pair an ELM327 adapter, open the free tier of the app and record both pedal and both throttle sensors through one slow full sweep. The pair that diverges tells you which part to buy, before you buy either.