P2138 — Throttle/Pedal Position Sensor/Switch “D”/”E” Voltage Correlation #

Note: The code description may vary depending on the vehicle manufacturer.

• P2138 — Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation (Generic, GM, Honda, Nissan, Toyota, Hyundai, Kia)
• P2138 — Accelerator Pedal Position Sensor Circuit Range/Performance (Subaru)
• P2138 — APP Sensor Plausibility Error (Volkswagen/Audi)
• P2138 — Throttle/Pedal Position Sensor/Switch D/E Voltage Mismatch (Mazda, Ford)

Summary of DTC P2138 #

P2138 indicates a mismatch or correlation error between the voltages of two accelerator pedal position sensors. These sensors, often called APP sensors (Accelerator Pedal Position sensors), communicate the pedal’s input to the engine control module (ECM or PCM). When the signals from the two sensors, labeled “D” and “E,” do not agree within a specified range, the ECM triggers this code to prevent possible unintended acceleration. This fault is a critical safety check, as modern vehicles use electronic throttle (“drive-by-wire”) systems instead of mechanical linkages. Identifying and addressing this issue promptly helps maintain safe and responsive vehicle operation.

Common Symptoms for DTC P2138 #

When P2138 is present, drivers often notice immediate changes in vehicle behavior. The severity can range from mild to significant, depending on the failure mode and OEM safety strategies. Here are the most frequent symptoms:

• Reduced engine power (“limp mode”)
• Check Engine Light (CEL) illuminated
• Unresponsive or erratic throttle response
• Engine may not accelerate above idle
• Possible traction control or stability system warnings
• Hard or delayed engine start (rarely)

Most Likely Causes for DTC P2138 #

P2138 usually arises when there’s an inconsistency between the two pedal sensors, but several root causes exist. Here they are, ranked from most to least common:

1. Faulty accelerator pedal position sensor assembly (internal sensor malfunction)
2. Wiring issues (damaged, corroded, loose, or pinched wires/connectors at the pedal sensor)
3. Faulty or poor electrical ground at the sensor or ECM
4. Water intrusion or contamination inside the pedal assembly connector
5. Faulty ECM/PCM (rare, usually after all other causes are eliminated)

Step-by-Step Diagnostic Guide for P2138 #

A careful, methodical approach is crucial to properly resolve P2138. Rushing can lead to misdiagnosis and unnecessary part replacement. Here’s a proven diagnostic process:

1. Verify the code with a scan tool and check for additional DTCs that may clarify the context.
2. Clear codes and perform a road test to see if P2138 returns immediately or is intermittent.
3. Visually inspect the accelerator pedal sensor and its connector for damage, corrosion, bent pins, or water intrusion.
4. Wiggle test the harness while observing sensor data with a scan tool to check for intermittent faults.
5. Monitor live data for both APP sensor voltages (often labeled APP Sensor 1 and 2 or D and E). They should rise smoothly and proportionally as the pedal is pressed.
6. Check for 5V reference and proper ground at the pedal connector using a multimeter.
7. If sensor voltages are inconsistent, replace the accelerator pedal assembly (sensor is usually not serviceable separately).
8. If wiring or connector issues are found, repair or replace affected components and retest.
9. If all else checks out, consider ECM/PCM diagnosis or replacement as a last resort.

Possible Repairs for P2138 #

Once the root cause is identified, effective repairs can be carried out. These should directly address the diagnosed issue:

• Replace the accelerator pedal position sensor assembly (most common and recommended by OEMs)
• Repair or replace damaged wiring or connectors between the pedal assembly and ECM
• Clean or dry the connector if water contamination is found, and apply dielectric grease as appropriate
• Restore or improve grounding connections for the sensor circuit
• Replace the ECM/PCM (rare, only after confirming all other possibilities)

Is It Safe to Drive with Code P2138? #

Driving with P2138 is generally not recommended. Most vehicles will enter a reduced power or “limp mode” to prevent unintended acceleration. This can severely limit speed and throttle response, creating unsafe driving conditions—especially in traffic or on highways. In rare cases, the vehicle may not accelerate at all. It’s best to address this issue promptly and avoid long-distance or high-speed driving until repairs are completed.

Vehicles Most Commonly Affected by P2138 #

While P2138 is a generic OBD-II code, it’s especially prevalent in certain makes and models due to similar drive-by-wire systems and pedal sensor designs. Here are some vehicles where P2138 is frequently reported:

• GM (Chevrolet, GMC, Cadillac, Buick, Pontiac, Saturn)
• Honda/Acura (Civic, Accord, CR-V, Odyssey)
• Nissan/Infiniti (Altima, Sentra, Rogue, Maxima, G35)
• Toyota/Lexus (Camry, Corolla, RAV4, Tacoma)
• Hyundai/Kia (Sonata, Elantra, Tucson, Optima)
• Volkswagen/Audi (Jetta, Passat, Golf, A3)
• Mazda (3, 6, CX-5, CX-9)
• Subaru (Forester, Outback, Impreza)

Common Mistakes & Best Practices for P2138 #

Even professional technicians can make missteps when diagnosing P2138. Avoid these pitfalls and follow these best practices:

• Don’t replace the accelerator pedal assembly without inspecting wiring and connectors—wiring faults are common and cheaper to fix.
• Always check for water intrusion at the pedal connector, especially after heavy rain or car washes.
• Use a scan tool to monitor live data—guesswork leads to unnecessary part swaps.
• Clear codes and retest after repairs to confirm the fix.
• Follow OEM diagnostic procedures and service bulletins for your specific vehicle.

Quick FAQ for DTC P2138 #

What does “voltage correlation” mean in this context?
Voltage correlation refers to the ECM comparing the outputs of two independent sensors inside the accelerator pedal. Both must track each other closely; any significant mismatch triggers the code to prevent unsafe throttle operation.

Can I clean or repair just the sensor instead of replacing the whole pedal?
On most vehicles, the pedal position sensor is integrated and not serviceable separately. OEMs usually require replacing the entire pedal assembly if the sensor is faulty.