I022

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The headlamp switch provides the IPC a Pulse Width Modulated (PWM) signal on CKT 8 whenever the Parklamp on signal CKT 9 is HI (Parklamp or headlamps "ON"). This PWM signal is derived from the dimming pot in the headlamp switch, with 0 duty cycle equalling max dim and Full duty cycle equalling full brightness. The IPC uses the PWM signal to control its incandescent lights and VF displays, as well as providing dimming output for the radio's VF display.

DTC I022 will set if the parklamp/headlamps are on and the PWM signal from the headlamp switch indicates a duty cycle less than 4%. The fault must be present for at least 2 seconds for the code to set. While the code is present, a substitute dimming value will be implemented to allow continued operation. ID42 however, will display the actual sensor reading. ID42 only updates while the parklamps or headlamps are "ON".

TEST DESCRIPTION

Test numbers refer to circled numbers on the diagnostic chart.

1. Headlights should be on during throughout checks in this tree, so that ID42 will continuously update.

2. Normal voltage at this point would be approximately 2.5 volts at max dim and 11.9 volts at full bright.

3. No voltage indicates loss of power or ground at the headlamp switch, or a bad switch assembly. Note: a grounded CKT 8 cannot cause this condition. Fuse "D13" would blow, causing the IPC to not realize the lights are on, and therefore the code would not be set.

4. Since the dim signal is correct at the headlamp switch, now check to see if the signal is making it to the IPC.

NOTES ON INTERMITTENTS

If an intermittent DTC 1022 is being set, turn headlamps "ON" and monitor ID42 while rotating dimmer switch through full travel, watching for sudden jumps. If the failure is induced, the reading will jump from its normal value to a reading below 4%. Also, insure good terminal contact at headlamp switch 4way connector and IPC Cavities "D3" & "C10". Manipulate the related wiring while observing IPC data value ID42.