Headlamps Suggested Message

TEST CONDITION(S)
1. Engine is running.
2. Twilight sentinel is not on.
3. Vehicle speed is greater than 20 mph.

FAILURE CONDITION(S)
1. Photocell indicating darkness is present.
2. Headlamps are off..

ACTION TAKEN
1. Display the HEADLAMPS SUGGESTED message on the IPC.
2. Activate the slow paced chime on the chime module.

DESCRIPTION
The PCM provides voltage to the twilight enable circuit, and the twilight enable switch provides the single path to ground. The BCM supplies the twilight enable circuit at pin 2B5, and it internally monitors the voltage level of the enable/delay circuit at pin 3C1. When the twilight sentinel is in the off position there will be a certain maximum resistance value in the enable/delay circuit, allowing very low voltage to reach pin 3C1 of the BCM. If the resistance value of the circuit is between the off position resistance value and the lowest resistance value of the twilight enable/delay circuit, the BCM is able to determine if the twilight sentinel is on or off. The BCM constantly supplies 5 volts to the twilight photocell circuit through pin 3C7. The twilight photocell acts like a variable resistor. When the photocell detects bright light it will have very low resistance, but if it detects darkness, the photocell will have very high resistance. The BCM also monitors the voltage level of the photocell circuit through pin 3C7. As the light detected by the photocell goes from bright to dark, the resistance in the circuit goes from low to high, and the voltage at pin 3C7 reaches a preset level, with the higher voltage being the darker setting, the BCM will know at what darkness level the headlamps should be turned on. The BCM will then check to see if the twilight sentinel is turned on or off. If the twilight sentinel is off, and all other failure conditions have been met, the BCM will send the TURN LIGHTS ON message to the IPC.

DIAGNOSIS
Condition Possible Cause
Message appears with headlamps on Open in CKT 1349
NO Message Short to ground in CKT 278
Short to voltage in CKT 1349
Shorted twilight photocell.
Message appears in daylight Open twilight photocell
Open in CKT 278