B3787

DTC B3787

CIRCUIT DESCRIPTION
Battery voltage is supplied directly to the ignition 3 relay. The body control module (BCM) controls the relay by grounding the control circuit through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the BCM. When the BCM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the BCM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage.

DTC DESCRIPTORS
This diagnostic procedure supports the following DTCs.
- DTC B3787 Blower Motor Relay Control Circuit Low
- DTC B3788 Blower Motor Relay Control Circuit High

CONDITIONS FOR RUNNING THE DTC
- The ignition voltage is between 9.0-18.0 volts.
- The BCM driver is activated for at least 0.5 seconds.

CONDITIONS FOR SETTING THE DTC
The BCM detects an improper voltage level on the output circuit that controls the ignition 3 relay for 1 second.

ACTION TAKEN WHEN THE DTC SETS
- The BCM stores the failure records.
- The ignition 3 relay output is disabled.

CONDITIONS FOR CLEARING THE DTC
- The DTC will become history if the BCM no longer detects a failure.
- The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
- The DTC can be cleared with a scan tool.

TEST DESCRIPTION

Steps 1 - 2:

Steps 3 - 9:

Steps 10 - 13:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for an audible click when the ignition 3 relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
3. Tests for voltage at the coil side of the ignition 3 relay.
4. Verifies that the BCM is providing ground to the ignition 3 relay.
5. Tests if ground is constantly being applied to the ignition 3 relay.
12. Perform the programming procedure for the BCM.