P1135

What Does Code P1135 Mean?

DTC P1135 signifies an intermittent fault detected within the Accelerator Pedal Position Sensor (APPS) ‘A’ circuit. The Engine Control Module (ECM), or Powertrain Control Module (PCM), monitors multiple dedicated voltage signals from the APPS to precisely interpret the driver’s throttle demand in drive-by-wire systems. The APPS typically incorporates two or more potentiometers or Hall-effect sensors, often designated ‘A’ and ‘B’, which generate redundant and opposing voltage signals (e.g., one increasing from 0.5V to 4.5V, the other decreasing from 4.5V to 0.5V as the pedal is depressed). The ECM continuously cross-references these signals for plausibility and consistency. Code P1135 is set when the ECM detects sporadic, momentary interruptions, unexpected spikes, drops, or inconsistent voltage readings within the ‘A’ circuit that do not correlate with the other sensor channels or with expected pedal movement, but are not a complete circuit failure. This intermittency implies a transient loss of signal integrity rather than a hard failure, making diagnosis potentially challenging. This subsystem directly affects throttle body actuation and overall engine power delivery.

Common Symptoms

• Intermittent or complete loss of throttle response, especially during acceleration.
• Sudden and unexpected engine surging or hesitation without driver input.
• Erratic or fluctuating idle speed.
• Vehicle entering “limp mode,” limiting engine RPM and vehicle speed.
• Illumination of the Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL).
• Difficulty maintaining a consistent speed (cruise control may disengage).

What Causes the Code P1135?

• Faulty Accelerator Pedal Position Sensor (APPS): Internal wear on the potentiometer tracks, faulty resistive elements, or intermittent internal circuit board issues are common causes for an erratic signal.
• Damaged Wiring Harness: Frayed, chafed, or broken wires within the APPS signal, reference voltage, or ground circuits can cause intermittent opens or shorts. This damage is often near flex points or areas susceptible to vibration.
• Corroded or Loose Electrical Connectors: Oxidation, bent pins, or inadequate terminal tension at the APPS connector or the corresponding ECM/PCM connector can lead to intermittent signal loss or resistance.
• Intermittent Short to Ground or Voltage: A compromised wire insulation could sporadically touch a grounded component or another power wire, causing momentary signal aberrations.
• ECM/PCM Internal Fault: While less common, an internal processing fault or intermittent power supply issue within the ECM/PCM itself could theoretically lead to misinterpretation of a valid APPS signal.

How to Diagnose and Troubleshoot

Diagnosis of an intermittent code like P1135 requires careful, systematic testing, often involving monitoring live data while attempting to induce the fault condition.

1. Retrieve and Document Freeze Frame Data: Use an OBD-II scan tool to retrieve the P1135 code and any associated freeze frame data. This data provides a snapshot of engine conditions (RPM, vehicle speed, engine load, APPS voltage) when the code was set, which can be invaluable for replication.
2. Visual Inspection:
   • Inspect the Accelerator Pedal Position Sensor (APPS) assembly for any physical damage or signs of foreign object intrusion.
   • Carefully trace the wiring harness from the APPS to the ECM/PCM, looking for any signs of chafing, cuts, pinches, corrosion, or rodent damage. Pay close attention to areas where the harness bends or passes through grommets.
   • Inspect the APPS electrical connector and the ECM/PCM connector for bent, pushed-back, or corroded pins. Check for proper terminal tension by gently tugging on individual wires while the connector is seated.
3. Scan Tool Live Data Monitoring:
   • Connect a scan tool and monitor the live data PIDs for “Accelerator Pedal Position Sensor A Voltage” (and B Voltage, if available).
   • With the ignition ON (engine OFF), slowly depress and release the accelerator pedal through its full range. Observe the voltage readings for smooth, linear changes without any sudden drops, spikes, or flat spots. For ‘A’ circuits, voltage typically increases steadily from approximately 0.5V at rest to around 4.5V at wide-open throttle (WOT).
   • While monitoring, perform a “wiggle test” on the APPS connector and the entire wiring harness. Gently flex, twist, and tap the harness sections, especially near connectors. Observe if the voltage readings fluctuate or drop intermittently.
   • If possible and safe, perform a road test while monitoring live data, attempting to replicate the conditions from the freeze frame data. Pay attention to voltage readings when symptoms occur.
4. Digital Multimeter (DMM) Testing (Out of Circuit):
   • Disconnect the APPS electrical connector.
   • Using a DMM, measure the resistance across the relevant potentiometer terminals of the APPS while slowly depressing the pedal by hand. Refer to the vehicle service manual for specific pinouts. Look for a smooth, consistent change in resistance without any open circuits or erratic readings.
5. DMM Testing (In Circuit / Back-probing):
   • With the APPS connected and ignition ON, carefully back-probe the APPS connector terminals to measure:
     • Reference Voltage: Verify a stable 5-volt reference voltage (Vref) from the ECM/PCM to the APPS. Fluctuation here can indicate ECM issues or wiring problems.
     • Ground: Confirm a solid ground connection. High resistance on the ground circuit can cause voltage offsets.
     • Signal Voltage: Back-probe the signal wire for the ‘A’ circuit. Slowly depress and release the pedal while observing the DMM. Look for smooth voltage transitions, similar to the scan tool test. Perform a wiggle test on the harness and connector during this measurement.
6. Continuity Test: If damage is suspected, disconnect both the APPS and ECM connectors. Perform a continuity test on each wire within the APPS circuit (signal, Vref, ground) from end to end. Check for shorts to ground or power on each wire.

Recommended Repairs and Solutions

Based on the diagnostic findings, the most common repairs for P1135 typically involve:

• Accelerator Pedal Position Sensor (APPS) Replacement: If direct testing of the sensor reveals internal intermittency or erratic output, replacing the entire APPS assembly is usually the most effective solution. Ensure the replacement part is an OEM equivalent or reputable aftermarket component.
• Wiring Harness Repair: If visual inspection or continuity tests identify a damaged section of the wiring harness, perform a professional wire repair. Use appropriate gauge wire, solder connections, and heat-shrink tubing for durability. Avoid using crimp connectors where possible, as they can also become intermittent over time.
• Connector Repair/Replacement: If the APPS or ECM/PCM connector exhibits bent pins, corrosion, or poor terminal tension, replace the affected connector or individual terminals. Clean any minor corrosion with electrical contact cleaner and a small brush.
• ECM/PCM Relearn Procedure: After replacing the APPS or performing significant repairs to the throttle control system, it is often necessary to perform a relearn or calibration procedure for the accelerator pedal and throttle body. Consult the vehicle’s service manual for specific steps, which may involve using a scan tool.
• Clear Codes and Verify Repair: After any repair, clear the DTCs from the ECM/PCM memory. Then, perform an extended road test under various driving conditions, including those from the freeze frame data, to confirm the intermittent fault does not return. Monitor live APPS data during this test to ensure smooth and consistent operation.