1998 Dodge Ram OBD-II Fault Codes P1688 and P1693: Fuel Pump Control Module & Companion Module Issues
The 1998 Dodge Ram is displaying OBD-II diagnostic trouble codes P1688 and P1693. These codes indicate potential issues with the Fuel Pump Control Module (FPCM) and a companion module, respectively. P1688: Fuel Pump Control Module (FPCM) Error This code is triggered when the FPCM, PCM memory, programming, or hardware detects an error while monitoring the fuel pump control system. The fault can occur both with the ignition on and engine off. Diagnostic Steps: 1. Turn the ignition to ON with the engine OFF. Use a DRBIII(R) scan tool to check for DTCs. If the Good Trip Counter for P1688 is displayed and not zero, proceed to step 2. If it is zero, replace the FPCM. Refer to the appropriate REMOVAL, OVERHAUL & INSTALLATION procedure. 2. Keep ignition ON with engine OFF. Use a scan tool to retrieve stored DTCs and record FREEZE FRAME data. Attempt to recreate the conditions observed in the FREEZE FRAME. Re-scan for DTCs. If P1688 reappears, replace the fuel injection pump. Refer to the appropriate REMOVAL, OVERHAUL & INSTALLATION guide. If the code does not return, the test is complete. P1693: Companion Module Error Detected This code indicates a detected fault in the companion module. It cannot exist independently and will typically be accompanied by other error codes in either the ECM or PCM. Recommended Action: Turn ignition ON with engine OFF. Clear all DTCs from the PCM using a scan tool. Then, check for stored DTCs in the ECM. Perform the appropriate test procedure for any stored errors. Complete TEST VER-2A as specified. Note: A reliable OBD-II scan tool is required to accurately retrieve and interpret these codes.
Is this vehicle equipped with a Cummins engine? The P1688 code indicates an issue with the Fuel Pump Control Module (FPCM), which is monitored during both ignition-on, engine-off and running conditions. This error may stem from hardware faults, memory errors, or programming issues in the FPCM or PCM. Diagnostic Procedure: 1. With the ignition ON and engine OFF, use a DRBIII(R) scan tool to check for DTCs. If the Good Trip Counter for P1688 is non-zero, proceed to step 2. If it's zero, replace the FPCM. Refer to the official REMOVAL, OVERHAUL & INSTALLATION guide. 2. Maintain ignition ON with engine OFF. Retrieve stored DTCs and FREEZE FRAME data. Attempt to reproduce the conditions recorded in the freeze frame. Re-scan for codes. If P1688 returns, replace the fuel injection pump. Refer to the appropriate service procedure. If the code does not return, testing is complete. For P1693: Companion Module Error Detected — this code cannot exist alone and will always be accompanied by other faults in either the ECM or PCM. Use a proper OBD-II scan tool to retrieve full diagnostic data before proceeding with repairs.