P1655

What Does Code P1655 Mean?

DTC P1655 is a manufacturer-specific diagnostic trouble code indicating a malfunction within the Starter Disable Control Circuit. This code is set by the Powertrain Control Module (PCM), also referred to as the Engine Control Module (ECM), when it detects an unexpected electrical state or an implausible signal in the circuit responsible for preventing engine cranking. The starter disable circuit is a critical safety and security feature designed to prevent the starter motor from engaging under specific conditions, such as when the vehicle’s security system (immobilizer) is active, when the transmission is not in Park or Neutral (P/N), or if the clutch pedal is not depressed (manual transmissions). The PCM monitors the voltage, current, or signal integrity of this circuit, often by interacting with other modules like the Body Control Module (BCM) or the Immobilizer Control Module. If the PCM detects that the disable signal is constantly active when it should be inactive, or vice versa, or if there’s an electrical fault like an open or short in the circuit, it will register P1655. This directly affects the vehicle’s starting system and can be indicative of issues within the security interlock system or transmission range sensing.

Common Symptoms

• No Crank/No Start Condition: The most prevalent symptom, where turning the ignition key or pressing the start button results in no response from the starter motor.
• Intermittent No-Start: The vehicle may start sometimes but fail to crank at other times, especially when cold or after sitting for a period.
• Security Light Illuminated: The vehicle’s security or immobilizer indicator light on the dashboard may be on or flashing.
• Check Engine Light (CEL) Illuminated: While P1655 is primarily a starting/security system code, it can trigger the Malfunction Indicator Lamp (MIL).

What Causes the Code P1655?

• Faulty Starter Disable Relay: An internal electrical fault within the relay that controls power to the starter solenoid, causing it to stick open or closed.
• Wiring Harness Issues: An open circuit, short to ground, short to voltage, or high resistance within the wiring connecting the PCM, starter disable relay, ignition switch, immobilizer module, or neutral safety switch/clutch interlock switch.
• Faulty Immobilizer Control Module (ICM) or Body Control Module (BCM): These modules may incorrectly send a “starter disable” signal to the PCM or starter relay, even when conditions for starting are met.
• Faulty Ignition Switch: Worn or damaged internal contacts in the ignition switch may not correctly send the “start” signal or fail to release the “accessory” or “run” signal properly.
• Faulty Transmission Range Sensor (TRS) / Neutral Safety Switch (NSS) or Clutch Pedal Position (CPP) Switch: An incorrect signal from these components, indicating the transmission is not in Park/Neutral or the clutch is not depressed, will prevent starter engagement.
• Blown Fuse: A blown fuse in the starter control circuit, ignition circuit, or security system circuit.
• Corroded or Loose Electrical Connections: Poor connections at the starter relay, PCM, BCM, or immobilizer module.
• Internal PCM/ECM Failure: Although less common, an internal fault within the PCM preventing proper monitoring or control of the starter disable circuit.

How to Diagnose and Troubleshoot

Diagnosis of P1655 requires a methodical approach, utilizing a digital multimeter (DMM) and an advanced OBD-II scanner capable of viewing live data and performing actuator tests.

1. Retrieve & Analyze Freeze Frame Data: Connect an OBD-II scanner to confirm P1655 and check for any related codes (e.g., U-codes related to communication, B-codes related to BCM or security). Analyze freeze frame data to understand the operating conditions (engine RPM, vehicle speed, engine temperature, etc.) when the code was set, which can provide clues about intermittent issues.
2. Perform a Thorough Visual Inspection: Begin by checking battery terminals for corrosion and ensuring they are tight. Inspect the battery’s state of charge (should be >12.6V static). Locate and visually inspect all fuses related to the starter, ignition, and security systems for any blown elements. Trace the wiring harness from the starter solenoid back to the starter relay, and from the relay to the PCM/BCM/Immobilizer module. Look for obvious signs of damage, chafing, bare wires, corrosion, or loose connections.
3. Verify Starter Disable Relay Operation:
   • Locate the starter disable relay in the under-hood or under-dash fuse box.
   • Using a wiring diagram, identify the power supply to the relay coil, the ground path, and the switched power path to the starter solenoid.
   • With the ignition on (but not attempting to crank), use a DMM to check for 12V at the relay coil’s power terminal.
   • Attempt to crank the engine while monitoring the ground side of the relay coil. The PCM/BCM should provide a ground signal to energize the relay. If no ground is present, the issue lies upstream in the control module or its inputs.
   • If the coil receives power and ground when commanded, remove the relay and test its continuity across the switched terminals using the DMM. Apply 12V and ground to the coil terminals to manually actuate the relay and confirm it clicks and switches continuity.
4. Test Inputs to the Control Modules:
   • Ignition Switch: Monitor live data with the scan tool for ignition switch position (Off, ACC, Run, Start) to ensure it correctly registers input.
   • Transmission Range Sensor (TRS)/Neutral Safety Switch (NSS): For automatic transmissions, verify the scan tool shows “Park” or “Neutral” when the shifter is in those positions. For manual transmissions, check the Clutch Pedal Position (CPP) switch via live data or directly with a DMM for proper continuity when the pedal is depressed.
   • Immobilizer Status: Some advanced scan tools can read the immobilizer status (e.g., “key recognized,” “immobilizer active/inactive”). Ensure it indicates the key is recognized and the immobilizer is inactive when attempting to start.
5. Perform Circuit Integrity Tests:
   • Disconnect the battery. Using wiring diagrams, identify the specific wires in the starter disable circuit between the PCM/BCM, immobilizer module, starter relay, and starter solenoid.
   • Test for continuity and resistance in each wire segment using a DMM. Look for high resistance (should be <0.5 ohms), opens (infinite resistance), or shorts to ground/voltage.
   • Check for proper ground integrity at all relevant modules and components using the DMM.

Recommended Repairs and Solutions

Once the root cause of P1655 has been identified through systematic diagnosis, the following repairs are typically performed:

• Replace Faulty Starter Disable Relay: If the relay fails the bench test or does not receive proper control signals, replacement is usually straightforward. Ensure the new relay matches the original specifications.
• Repair or Replace Damaged Wiring: If an open, short, or high resistance is found in the wiring harness, perform professional wiring repair using appropriate gauge wire, solder, and heat-shrink tubing. If the damage is extensive, consider replacing the entire harness segment. Always ensure connections are clean and secure.
• Replace Immobilizer Control Module (ICM) or Body Control Module (BCM): If diagnostic steps confirm that one of these modules is sending an erroneous starter disable signal, replacement and subsequent programming (which often requires specialized dealer tools) will be necessary. This is a complex repair best left to qualified technicians.
• Replace Faulty Ignition Switch: If the ignition switch is not providing the correct signals, replace it according to manufacturer specifications. Ensure proper wire routing and connection.
• Replace Transmission Range Sensor (TRS) / Neutral Safety Switch (NSS) or Clutch Pedal Position (CPP) Switch: If these interlock switches are found to be faulty, replace them. For TRS/NSS, ensure proper adjustment if required by the manufacturer, as incorrect adjustment can lead to intermittent no-start conditions.
• Check and Replace Blown Fuses: Always replace blown fuses with new ones of the correct amperage. A fuse that repeatedly blows indicates a short circuit that must be located and repaired.
• PCM/ECM Replacement/Reprogramming: Only consider PCM/ECM replacement as a last resort, after all other components and wiring have been thoroughly tested and ruled out. PCM replacement requires specific programming to the vehicle’s VIN and immobilizer system.

Mechanic’s Tip: After any repair, clear the DTCs with the OBD-II scanner and attempt to start the vehicle multiple times. If the issue was intermittent, perform several drive cycles and power cycles to confirm the repair is successful and the code does not return. Pay attention to any security warning lights on the dash that may appear after component replacement, as these often indicate the need for system relearning or programming.