B3788

DTC B3788

CIRCUIT DESCRIPTION




Battery voltage is supplied directly to the after blow relay directly through the underhood fuse block. The body control module (BCM), provides the ground to enable the after blow operation through the blower motor relay control circuit. The after blow relay control circuit and relay are retailer installed. The BCM provides logic to enable the blower based on information from the engine control module (ECM) or powertrain control module (PCM). The duration of the after blow relay cycle is determined by A/C operation, ambient air temperature and vehicle speed.

CONDITIONS FOR RUNNING THE DTC
- Engine is running.
- Any of the conditions for setting the DTC are met for 5 seconds.
- Battery voltage is between 11 to 18 volts.
- Output control is OFF.
- Output control is ON.

CONDITIONS FOR SETTING THE DTC

B3787
The BCM detects a short to ground for 5 seconds on the blower motor relay control circuit when the output is OFF.

B3788
The BCM detects a short to battery for 5 seconds on the blower motor relay control circuit when the output is ON.

ACTION TAKEN WHEN THE DTC SETS
- The BCM will not illuminate the malfunction indicator lamp (MIL).
- The BCM stores the Failure Records.
- The HVAC blower is disabled.

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

DIAGNOSTIC AIDS
- Visually inspect the relay and connection for damage.
- Visually inspect the instrument panel fuse block for damage.
- Check for poor connection at the BCM.
- Refer to Testing for Intermittent and Poor Connections in Diagnostic Aids.

TEST DESCRIPTION

Steps 1-13:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for an audible click when the after blower relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
3. Tests for voltage at the coil side of the after blow relay. The BATT Feed fuse supplies power to the coil side of the after blow relay.
4. Verifies that the body control module is providing ground to the after blow relay.
5. Tests if ground is constantly being applied to the after blow relay.
6. Tests if intermittent voltage is being applied to the after blow relay.
12. It is important to follow the programming procedure for replacing the body control module.