Code 55 - Faulty ECM Signals
Fig 1: Flow Chart, Code 55 - Grounded Voltage Reference, High Voltage on Oxygen (O2) Sensor Circuit or ECM
NOTE:
Check for corrosion at ECM edgeboard connector and terminals. If present, check for coolant sensor, windshield or heater core leaks. Repair leak, clean connector terminals and replace ECM. Also, check for 4-terminal EST harness being too close to electrical signals, such as spark plug wires, distributor housing, generator, etc.