Powertrain Diagnosis

Diagnostic Chart:

Wiring Diagram:

The powertrain control module (PCM) monitors the resistance of the fuel level sensor (tank sender), calculates the amount of fuel in the tank, and provides a pulse width modulated (PWM) ground to control the fuel gauge. The duty cycle increases to move the gauge to full (approximately 86%) and decreases (approximately 15%) to command EMPTY. During the three-second key-on bulb check, the PCM commands the fuel gauge to 0% duty cycle and turns on the LOW FUEL telltale. The diagnostic test is performed only when the gauge is commanded to a 0% duty cycle (e.g., during key-on bulb check period or if P0462 or P0463 are set). DTC P0656 will set if the commanded duty cycle is zero and the output feedback is low (it should be high/ignition voltage).

DTC PARAMETERS
DTC P0656 will set if the commanded duty cycle is zero percent and:
^ Output feedback is less than 3.0 volts.
^ Longer than one second.

IMPORTANT: If the output circuit is shorted to battery voltage, the fuel gauge will be forced to 0% duty cycle and the LOW FUEL telltale state (On or OFF) will depend on actual fuel level.

DIAGNOSTIC AIDS
A corroded or loose connection at any of the terminal locations can cause DTC P0656.

If the output is shorted to ground, the fuel gauge will read full or slightly past full. If the output is open, gauge will read empty or slightly below. In either case, the LOW FUEL telltale will be commanded On, only if P0656 is set (to set a P0656, the PCM must be commanding a 0% duty cycle, e.g., during key-on bulb check). An intermittent problem in the circuit will likely result in a customer complaint of fuel gauge inaccuracy rather than a P0656 being set.

The Scan tool may be used to command the fuel gauge (special test-Instrument Cluster section) and the low fuel telltale (special test-QDM test).