P1515

What Does Code P1515 Mean?

DTC P1515, commonly interpreted as “Electric Current Circuit Malfunction,” indicates that the Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected an irregular or unexpected current draw within a specific monitored electrical circuit. While the exact circuit can vary by manufacturer and vehicle model, for many applications, particularly General Motors vehicles, P1515 is frequently associated with the Throttle Actuator Control (TAC) module or motor circuit. The ECM/PCM continuously monitors the current flowing through actuators such as the TAC motor to ensure proper operation and detect faults. If the actual current draw deviates significantly from the calibrated reference range – either too high (indicating a short or excessive load) or too low (indicating an open circuit or insufficient load) – for a predetermined period, the ECM/PCM will set P1515. This signifies a potential internal fault within the actuator, wiring integrity issues, or an excessive mechanical load preventing the actuator from performing its commanded function accurately. This fault directly impacts the electronic throttle body (ETB) system, which is critical for precise engine speed and load control.

Common Symptoms

• Malfunction Indicator Lamp (MIL) Illumination: The check engine light will be illuminated.
• Reduced Engine Power / Limp Home Mode: The ECM may command a reduced power mode to prevent further damage, severely limiting vehicle speed and acceleration.
• Erratic or Rough Idle: The engine may idle unstably or at an unusually high or low RPM.
• Engine Stalling: The engine may stall, especially during idle or deceleration.
• Poor Throttle Response: The vehicle may exhibit hesitation, lack of acceleration, or inconsistent reaction to accelerator pedal input.
• No Start Condition: In severe cases, the engine may not start at all.

What Causes the Code P1515?

• Faulty Throttle Actuator Control (TAC) Motor/Module: Internal wear, short circuits, open windings, or carbon buildup within the electric motor itself, preventing smooth operation or causing incorrect current draw.
• Wiring Harness Issues: Damaged, chafed, corroded, or shorted wires within the TAC motor circuit, including open circuits, shorts to ground, or shorts to voltage. Compromised insulation can lead to intermittent faults.
• Poor Electrical Connections: Loose, corroded, or damaged pins within the TAC module/motor connector or the ECM/PCM connector.
• Excessive Mechanical Resistance in Throttle Body: Accumulation of carbon deposits, debris, or a binding throttle plate shaft that creates excessive friction, causing the TAC motor to draw abnormally high current.
• Ground Circuit Malfunction: An insufficient or intermittent ground connection for the TAC module or motor.
• ECM/PCM Internal Fault: Although less common, an internal failure of the ECM/PCM’s driver circuit responsible for controlling or monitoring the TAC system current.

How to Diagnose and Troubleshoot

Diagnosis of P1515 requires a systematic approach using specialized tools and an understanding of electrical circuits.

1. Visual Inspection: Begin by thoroughly inspecting the throttle body and its immediate surroundings. Check for any obvious signs of damage, physical obstructions, or excessive carbon buildup that might impede throttle plate movement. Examine the entire wiring harness leading to the throttle body/TAC module for any visible signs of fraying, cuts, chafing, or corrosion, particularly near connectors.
2. OBD-II Scan Tool Analysis:
   • Connect a diagnostic scan tool and retrieve all stored and pending Diagnostic Trouble Codes (DTCs). Note any other related codes.
   • Access live data streams. Monitor parameters such as “Desired Throttle Angle,” “Actual Throttle Angle,” “Throttle Position Sensor (TPS) 1 Voltage,” “TPS 2 Voltage,” and “TAC Motor Current.”
   • Actuate the throttle plate (if the scan tool supports bidirectional control) while monitoring the actual throttle angle and motor current. Look for discrepancies between desired and actual, erratic TPS readings, or motor current readings that are outside the manufacturer’s specified range during actuation.
3. Battery Voltage Verification: Ensure the vehicle’s battery voltage is stable and within specification (typically 12.6V or higher). Low system voltage can sometimes trigger false electrical fault codes.
4. Power and Ground Circuit Integrity Check (TAC Module/Motor):
   • With the ignition OFF, disconnect the electrical connector from the throttle body/TAC module.
   • Using a Digital Multimeter (DMM), set to voltage mode, turn the ignition ON and check for proper battery voltage supply (typically 12V) at the appropriate power supply pin(s) of the connector. Refer to the vehicle’s wiring diagrams for correct pin identification.
   • Still with the connector disconnected, set the DMM to resistance (ohms) mode and check for a good ground connection at the appropriate ground pin(s). Resistance to chassis ground should be less than 5 ohms. A high resistance or open circuit indicates a faulty ground.
5. Continuity and Resistance Check (TAC Motor Control Wires):
   • Ensure the vehicle’s battery is disconnected.
   • Disconnect the electrical connector from both the throttle body/TAC module and the ECM/PCM (if the wires run directly between them).
   • Using a DMM, check the resistance of each individual TAC motor control wire end-to-end. Compare the readings to factory specifications. An “OL” (open line) reading indicates an open circuit, while a very low resistance (near 0 ohms) could indicate a short between wires.
   • Check for shorts to ground and shorts to voltage on all TAC circuit wires by measuring resistance from each wire to chassis ground and to the positive battery terminal (or a known B+ source, with ignition OFF).
6. Throttle Actuator Motor Resistance (if serviceable): If the TAC motor is a separate, serviceable component, measure its internal resistance directly using a DMM. Compare this reading to the manufacturer’s specified resistance range. An out-of-specification reading confirms an internal motor fault.
7. PCM/ECM Pin-out Voltage Check: If all other circuit checks pass, carefully back-probe the ECM/PCM connector pins for the TAC circuit while the system is operational (if safe to do so) to verify that the ECM/PCM is sending the correct command signals and monitoring the return signals as expected. This step is typically performed last to isolate an internal PCM fault.

Recommended Repairs and Solutions

The repairs for P1515 are directly correlated with the root cause identified during diagnosis:

1. Clean the Throttle Body: If carbon buildup or debris is found to be impeding the throttle plate’s movement, thoroughly clean the throttle body using a specialized throttle body cleaner. Ensure all moving parts are free from obstruction. After cleaning, perform any necessary throttle body relearn procedures as specified by the vehicle manufacturer.
2. Repair or Replace Wiring and Connectors: If damaged, corroded, shorted, or open wiring or connectors are identified in the TAC motor circuit, these components must be repaired or replaced. Use appropriate automotive-grade wire, connectors, and crimping/soldering techniques to ensure durable, reliable connections.
3. Replace the Throttle Actuator Control (TAC) Module/Motor or Complete Throttle Body: In most modern drive-by-wire systems, the TAC motor, along with the throttle position sensors, are integrated into the throttle body assembly. If internal motor resistance is out of specification, or if power, ground, and wiring checks are all confirmed good but the system continues to malfunction, the entire throttle body assembly will likely need to be replaced. Always ensure proper relearn procedures are executed after throttle body replacement to calibrate the new unit with the ECM/PCM.
4. Address Mechanical Resistance: Any mechanical binding within the throttle body assembly, external linkages (if applicable), or even a bent throttle plate shaft, must be resolved. This may necessitate replacement of the entire throttle body.
5. PCM/ECM Replacement: ECM/PCM replacement should only be considered as a last resort, after all other components and wiring have been meticulously tested and ruled out as the source of the fault. If an internal PCM driver fault is confirmed, ensure the new module is properly programmed to the vehicle’s VIN and options.