P1651 - FAULT CODE - OBD2

POST UPDATED IN January, 2023

P1651 Code failures by brands

P1651 BUICK, CADILLAC, CHEVROLET, GMC, PONTIAC, SATURN: FAN 1 RELAY CONTROL CIRCUIT

Description of DTC code P1651

The vast majority of vehicles employ fans with electric motors so that the temperature of the car’s engine is maintained at the proper levels to achieve good engine performance.

ODMs (Output Driver Modules) are used by the Powertrain Control Module (PCM) to activate or turn on various current-driven devices, which are necessary to control many engines and transaxle functions. Each ODM can control up to 7 separate outputs by applying ground to the device that the PCM activates.

Unlike the QDMs (Quad Driver Modules) previously employed, the ODMs have the capability to diagnose each output circuit individually. The P1651 OBDII fault code is set when an improper voltage level is found on the ODM B output that controls the fan 1 relay.

Symptoms of fault code P1651

  • Check Engine lamp illuminated.
  • Problems arising from the starter motor.
  • Problems with the gears.
  • Unstable engine.
  • Low voltage.

Causes of OBD2 P1651

The factors by which the P1651 OBD2 diagnostic code is stored are:

  • Wires or connectors on the PCM or Fan 1 relay could be damaged.
  • Powertrain Control Module connections could be faulty.
  • The fan relay may be faulty.
  • Low or dirty oil.

Possible solutions of the DTC code P1651

The steps to follow to correct the DTC P1651 OBDII code are:

  • Consult the TSBs as a first step.
  • Inspect the relay circuit connectors to check for corroded or damaged terminals. If such conditions are found, make corrections.
  • Disconnect the PCM and with the key in the ON position, use a voltmeter connected to the fan relay circuit to check if the connections are in good condition. While observing the readings given by the voltmeter, move the connectors and wires related to the relay. A voltage change indicates the location of the fault.

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