Low Brake Fluid and Brake Telltale

Brake Fluid Level Switch Circuit:

CIRCUIT DESCRIPTION:
The BCM supplies 5 volts to the low brake fluid circuit and the brake fluid level switch provides the single path to ground. The BCM supplies and internally monitors the voltage level of the circuit at pin "1D2." When the brake fluid switch is open, the BCM will detect 2.5 volts due to the switches internal resistor. If the brake fluid switch provides a path to ground (low brake fluid condition present), the BCM will detect low voltage (less than 1.5 volts). If the condition exists for at least 3 seconds, the BCM will send the "LOW BRAKE FLUID" message to the CCDIC.

If the BCM detects a voltage greater than 3.5 volts at pin "1D2" for more than 3 seconds, it will send the "SERVICE BRAKE FLUID SWITCH" message to the CCDIC.

TEST CONDITION(S):
1. Ignition 3 "ON."

FAILURE CONDITION(S):
Low brake fluid level exists for at least 3 seconds (voltage less than 1.5 volts).

ACTION TAKEN:
1. Turn on "BRAKE" telltale on IPC.
2. Display the "LOW BRAKE FLUID" message on the CCDIC.

DIAGNOSIS:

Condition Possible Causes

Erroneous Message Short to ground on CKT 853, or shorted switch

No Message Open in CKT 853 or CKT 736 or open in switch