DTC 73

Circuit Description

The LED Display Dimming Output Circuit receives its ground in the form of a PWM output from the CCM through CKT 1382. The power for the circuit is supplied internally from the light switch, HVAC control head, and radio control head.

When the CCM is powered up, CKT 1382 is pulled low. If, after 60 milliseconds, the CCM senses the line to be high, Code 73 will set.

Test Description

Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test checks for a short to B+ in CKT 1382.
2. This test checks for proper operation at the radio control head end of the circuit.
3. This test puts the Radio Control Head back into the circuit, which has checked OK up to this point. If the code resets, the Radio Control Head must be causing it and should be replaced.
4. This test puts the Light Switch LED back into the circuit. If the code resets, the Light Switch Assembly must be causing it and should be replaced.
5. This test puts the (optional) C68 HVAC Control Head back into the circuit. If the code resets, the HVAC Control Head must be causing it and should be replaced.

Diagnostic Aids

If the code is a history code, the problem may be intermittent. Try performing the tests shown while "wiggling" wiring and connectors; this can often cause the fault to appear. Check for poor connections at the CCM, the radio control head, and the HVAC control head (if equipped with C68 Electronic Climate Control); these could cause an open or an intermittent fault. Refer to "Intermittents/Poor Connections".

This code will only set if the dimming request IS NOT 0% (full bright) or 100% (full dim). Also, the dimming circuit must be active for the code to set, i.e., the headlamps or parking lamps must be "ON" and some level of dimming must be requested.

If CKT 1382 is shorted to battery, none of the LEDs will operate.