P2138 — Throttle/Pedal Position Sensor/Switch « D »/ »E » Voltage Correlation

The Diagnostic Trouble Code (DTC) P2138 indicates a problem with the voltage correlation between the throttle pedal position sensors, specifically switches « D » and « E ». In simple terms, it means the car’s Engine Control Unit (ECU) has detected an inconsistency or malfunction in the signals coming from these sensors, which are responsible for measuring the position of the accelerator pedal. Keep in mind that labels for this code may vary slightly depending on the vehicle manufacturer, but the underlying issue is always related to pedal sensor signals.

Fast Facts

System affected: Throttle Control / Pedal Position Sensors
Severity: Moderate to High
Main symptoms: Check Engine Light, Reduced Power, Throttle Response Issues
Driveability: Limited — vehicle may operate but with constraints

Manufacturer variations for trouble code P2138

Different vehicle manufacturers may use slightly different labels or code formats to identify similar issues related to the pedal position sensors. The core problem with code P2138, however, remains consistent—it’s always about the voltage correlation between specific throttle pedal sensors.

Ford: P2138 — « Throttle/Pedal Sensor ‘D’/’E’ Voltage Correlation »
Volkswagen: 5F7D — « Pedal Position Sensor Signal Error »
BMW: 2A81 — « Throttle Pedal Sensor Signal Malfunction »
Toyota: P2138 — « Throttle Pedal Sensor Circuit Range/Performance »
Honda: P2138 — « Throttle Position Sensor Correlation Issue »

What does trouble code P2138 mean?

In very simple terms, P2138 indicates that the ECU (the vehicle’s onboard computer) has detected an inconsistency or fault in the signals being sent from the pedal position sensors—specifically the « D » and « E » switches or signals, which are part of the electronic throttle control system. The throttle pedal position sensors are responsible for informing the ECU about how much the driver is pressing the accelerator pedal. These sensors typically work in pairs or sets to improve accuracy and safety.

The ECU constantly monitors these sensors’ voltages to ensure they are within expected ranges and that both sensors agree with each other. When the ECU detects that the signals from these sensors are not correlating correctly—either due to a discrepancy or a fault—this code is triggered. Usually, it points to a mechanical or electrical issue with the sensors, wiring, or related components.

The triggers for this code often occur during driving when sensors fail to provide consistent signals, or during a routine diagnostic check, revealing the inconsistency. In some vehicles, this may also come up after a sensor replacement or if there’s a recent repair involving the throttle body or pedal assemblies.

Severity and risks of trouble code P2138

The presence of P2138 can range from a minor inconvenience to a more serious issue affecting vehicle performance. Typically, this code indicates a problem that can affect how smoothly the engine responds to accelerator inputs. If the ECU detects that the pedal sensors are giving conflicting signals, it may activate a safety mode.

**Potential risks include:**

Reduced acceleration or unexpected acceleration
Loss of throttle control, leading to poor drivability
Potential for engine stalling or hesitation
Increased emissions and fuel consumption

**Is the vehicle safe to drive?** Limited — the vehicle can typically be driven, but with caution. It’s advisable to have the issue diagnosed and repaired promptly to prevent unexpected breakdowns or safety concerns.

Symptoms of trouble code P2138

When this code is active, you may notice various symptoms, although some vehicles might experience only mild issues. Common symptoms include:

Illuminated Check Engine Light (CEL): on the dashboard, indicating an active fault.
Inconsistent acceleration: feeling hesitation or surges when pressing the accelerator pedal.
Reduced engine power: the vehicle may enter a ‘limp mode’ to protect itself.
Erratic or unresponsive throttle: delayed or abnormal responses when pressing on the accelerator.
Engine stalling or rough idling: especially during startup or low-speed driving.

Most likely causes of trouble code P2138

Understanding the underlying causes can help streamline diagnostics and repairs. Generally, causes can be grouped by their nature:

Faulty pedal position sensors or switches: a malfunction within the sensors themselves, or worn-out components.
Damaged or corroded wiring and connectors: loose, frayed, or corroded wiring can lead to signal inconsistencies.
Problems with the throttle pedal assembly: mechanical issues or misalignment affecting sensor readings.
Issues within the ECU or related modules: although less common, internal electronic faults can cause correlation problems.
Software glitches or updates needed: in rare cases, a firmware refresh can fix false positives.

How to diagnose trouble code P2138

Proper diagnosis requires a systematic approach, focusing on both electrical and mechanical components. Here are generic, safe steps to identify the cause:

Perform a visual inspection: check wiring harnesses, connectors, and the pedal assembly for obvious damage, corrosion, or disconnection.
Use a scan tool to read live data: compare the pedal position sensor signals « D » and « E » while gently pressing the pedal to see if the data is consistent and within expected ranges.
Check for other stored codes: to identify related issues, such as throttle body or sensor faults.
Inspect the pedal assembly and sensors physically: ensure the sensors are properly mounted, aligned, and free of debris or damage.
Test wiring continuity: to confirm that wiring between sensors, connectors, and ECU is intact and has no shorts or opens.
Verify sensor voltage signals: use a multimeter to check the supply and signal voltages at the sensors’ connector for abnormal readings.
Perform a sensor swap test: if possible, swap the pedal sensors with known good units to see if the fault persists or moves with the sensor.

Possible repairs for trouble code P2138

Addressing P2138 often involves both electrical and mechanical repairs. Here are common repair strategies:

Replace or recalibrate pedal position sensors: if sensors are faulty or out of spec. This step is typically performed by a professional.
Repair or replace damaged wiring and connectors: to restore proper electrical integrity. Basic repair options are available but often require professional expertise.
Inspect and fix the pedal assembly: realign or repair the pedal mechanism if mechanical issues are detected.
Update vehicle firmware: if a software glitch is suspected, a technician can perform ECU updates or reflashing.
Replace the entire pedal assembly: in cases of severe mechanical or sensor failure, especially if sensor replacement alone does not resolve the issue.

Vehicles commonly associated with trouble code P2138 in Europe

While specific models and engine types vary, certain brands and vehicle profiles tend to encounter this fault more frequently in Europe:

Volkswagen Group: including VW Golf, Passat, Audi models with electronic throttle control.

Ford: Focus, Fiesta, and Mondeo with pedal sensor or throttle system issues.

BMW: 1 Series, 3 Series, and other models equipped with electronic throttle control.

Toyota: Corolla, Yaris, and other models with electronic throttle systems.

Honda: Civic, CR-V, other models using electronic throttle sensors.

Frequent mistakes with trouble code P2138

Diagnostic and repair procedures can sometimes be hindered by common mistakes. Awareness of these can save time and prevent further issues:

Ignoring connector condition: failure to inspect wiring and connectors may lead to misdiagnosis.
Replacing sensors without verifying the root cause: sensors can sometimes be fine, but wiring or ECU issues are the actual cause.
Disregarding software updates: an outdated ECU firmware might cause false triggers or unresolved faults.
Overlooking other related codes: ignoring related DTCs may prevent addressing the actual problem effectively.
Not using proper diagnostic tools: reliance on generic tools might miss detailed live data needed for accurate diagnosis.

FAQ — trouble code P2138

Can this code disappear on its own?

Typically, P2138 does not resolve spontaneously. It requires diagnosis and repair. However, if the fault clears and conditions improve, the code might temporarily extinguish, but it often returns unless the root cause is addressed.

Can I keep driving?

Yes, in most cases, the vehicle can be driven with this fault, but likely with limited engine power or response. It is advisable – for safety and future reliability – to have it inspected soon.

Why does the code return after clearing?

The code reappears because the underlying issue—such as faulty sensors, wiring, or calibration—is still present. Clearing the code only resets the dashboard alert temporarily.