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
The numbers below refer to the step numbers on the diagnostic table.
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Listen for an audible click when the ignition 3 relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
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Tests for voltage at the coil side of the ignition 3 relay.
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Verifies that the BCM is providing ground to the ignition 3 relay.
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Tests if ground is constantly being applied to the ignition 3 relay.
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Perform the programming procedure for the BCM.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views | |||
1 | Did you perform the HVAC Diagnostic System Check? | Go to Step 2 | |
Does the ignition 3 relay turn ON and OFF with each command? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 | |
Does the test lamp illuminate? | Go to Step 4 | Go to Step 10 | |
Does the test lamp turn ON and OFF with each command? | Go to Step 8 | Go to Step 5 | |
Does the test lamp remain illuminated with each command? | Go to Step 7 | Go to Step 6 | |
6 | Test the control circuit of the ignition 3 relay for a short to voltage and an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
7 | Test the control circuit of the ignition 3 relay for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 9 |
8 | Inspect for poor connections at the ignition 3 relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
9 | Inspect for poor connections at the harness connector of the body control module (BCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 12 |
10 | Repair the battery positive voltage circuit of the ignition 3 relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 13 | -- |
11 | Replace the ignition 3 relay. Did you complete the replacement? | Go to Step 13 | -- |
|
Important: : Perform the programming procedure for the BCM. Replace the BCM. Refer to Body Control Module Replacement in Body Control System. Did you complete the replacement? | Go to Step 13 | -- | |
13 |
Does the DTC reset? | Go to Step 2 | System OK |
