Circuit Description
The Cooling Fan Relay 1 or RAD FAN LOW relay, and Cooling Fan Relay 2 or RAD FAN HI relay are controlled by the engine control module (ECM). Battery positive voltage is supplied to the relay coil. The ECM monitors the voltage level on the control circuit of the relay. When the relay is off, voltage level should be near battery voltage on the control circuit of the relay. When the relay is commanded on, voltage level will be low on the control circuit of the relay. The ECM will provide ground on the control circuit of the relay using a low side driver. If the ECM detects a improper voltage level on the control circuit of the relay, a DTC will set.
DTC Descriptor
This diagnostic procedure supports the following DTCs:
| • | DTC P0480 Cooling Fan Relay 1 Control Circuit |
| • | DTC P0481 Cooling Fan Relay 2 Control Circuit |
Conditions for Running the DTC
| • | The ignition is ON or the engine is operating. |
| • | The ignition 1 voltage is more than 10 volts. |
| • | DTCs P0480 and P0481 run continuously once the above conditions are met. |
Conditions for Setting the DTC
The ECM detects one of the following conditions on the control circuit of one of the relays:
| • | An open |
| • | A short to ground |
| • | A short to voltage |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
Conditions for Clearing the MIL/DTC
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
| • | For an intermittent condition, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | The following tables illustrate the RAD FAN LOW relay and RAD FAN HIGH relay terminal locations in the underhood fuse block: |
RAD FAN LOW Relay Terminal Identification | |
|---|---|
Low Speed Cooling Fan Supply Voltage | Ignition 1 Voltage |
Control | B+ Switch |
Front of Vehicle | |
RAD FAN HI Relay Terminal Identification | |
|---|---|
High Speed Cooling Fan Supply Voltage | Ignition 1 Voltage |
Control | B+ - Switch |
Front of Vehicle | |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
A test lamp that remains illuminated indicates a short to ground on the control circuit. A test lamp that does not illuminate indicates an open or short to voltage on the control circuit.
-
This step tests the control circuit for high resistance.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Cooling Schematics Connector End View Reference: Cooling System Connector End Views | ||||||||||
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls in Engine Controls - 1.6L (L91) or Diagnostic System Check - Engine Controls in Engine Controls 2.0L (L34 GMDAT) | ||||||
2 |
Does the RAD FAN LOW relay turn ON and OFF with each command? | -- | Go to Step 3 | Go to Step 4 | ||||||
3 | With a scan tool, command the Fan High Speed ON and OFF. Do the RAD FAN HI relay turn ON and OFF with each command? | -- | Go to Diagnostic Aids | Go to Step 4 | ||||||
4 |
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 13 | ||||||
5 |
Does the test lamp turn ON and OFF? | -- | Go to Step 7 | Go to Step 6 | ||||||
Does the test lamp remain illuminated? | -- | Go to Step 9 | Go to Step 10 | |||||||
7 |
Is the resistance less than the specified value? | 3 ohms | Go to Step 8 | Go to Step 13 | ||||||
Important: Use a test lamp that measures between 25-30 ohms for this test. Is the voltage less than the specified value? | 2.5 V | Go to Step 11 | Go to Step 10 | |||||||
9 | Test the control circuit of the affected 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 16 | Go to Step 12 | ||||||
10 | Test the control circuit of the affected relay for one of the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12 | ||||||
11 | Test for shorted terminals and poor connections at the affected relay. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14 | ||||||
12 | Test for shorted terminals and poor connections at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 15 | ||||||
13 | Repair the open, short to ground, or high resistance on the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- | ||||||
14 | Replace the affected relay. Refer to Relay Replacement in Wiring Systems. Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||
15 | Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls - 1.6L (L91) or Engine Control Module Replacement in Engine Controls - 2.0L (L34 GMDAT). Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||
16 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 17 | ||||||
17 | Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List in Engine Controls - 1.6L (L91) or Diagnostic Trouble Code (DTC) List in Engine Controls - 2.0L (L34 GMDAT) | System OK | ||||||
