Circuit Description
Ignition voltage is supplied directly to the cooling fan relay coil. The engine control module (ECM) controls the relay by grounding the control circuit via an internal switch called a driver. The primary function of the driver is supply the ground for the component being controlled. Each driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be low (near 0 volts). When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high (near battery voltage). If the fault detection circuit senses a voltage other than what is expected, the fault line status will change causing the DTC to set. The relay is used to control the high current flow to the cooling fan motors. This allows the ECM driver to only have to handle the relatively low current used by the relay.
DTC Descriptor
This diagnostic procedure supports the following DTCs:
| • | DTC P0480 Cooling Fan Relay Low Speed Circuit Fault |
| • | DTC P0481 Cooling Fan Relay High Speed Circuit Fault |
Conditions for Running the DTC
Ignition switch is ON.
Conditions for Setting the DTC
An open or a short to battery/ground condition in the cooling fan control circuit exists.
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. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn off at the end of 3 consecutive validation cycles in which the diagnostic runs without a fault. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
Using Freeze Frame and/or failure records data may aid in locating an intermittent condition. If the DTC cannot be duplicated, the information included in the Freeze Frame and/or failure records data can be useful in determining how many miles since the DTC set. The fail counter and Pass Counter can also be used to determine how many ignition cycles the diagnostics reported a Freeze Frame conditions (rpm, load, vehicle speed, temperature, etc.) that are noted. This will isolate when the DTC failed.
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 - Vehicle? | -- | Go to Step 2 | |
2 |
Does the relay turn ON and OFF with each command? | -- | Go to Step 3 | Go to Step 5 |
3 |
Does the amperage measure less than the specified value? | 0.75 amps | Go to Diagnostic Aids | Go to Step 4 |
4 |
Does the DVM display infinite resistance? | -- | Go to Step 12 | Go to Step 10 |
5 |
Does the test light turn ON and OFF with each commanded? | -- | Go to Step 8 | Go to Step 6 |
6 |
Does the test light illuminate? | -- | Go to Step 7 | Go to Step 11 |
7 |
With a fused jumper wire connected to ground, probe the relay control circuit in the ECM harness connector. Does the relay operate? | -- | Go to Step 9 | Go to Step 10 |
8 | Check the connections at the relay. Is a problem found and corrected? | 2.5 V | Go to Step 14 | Go to Step 12 |
9 | Check the connection at the ECM. Is a problem found and corrected? | -- | Go to Step 11 | Go to Step 13 |
10 | Repair the faulty relay control circuit. Is the repair complete? | -- | Go to Step 14 | -- |
11 | Repair the faulty relay ignition feed circuit. Is the repair complete? | -- | Go to Step 14 | -- |
12 | Replace the relay. Is the replacement complete? | -- | Go to Step 14 | -- |
13 | Replace the ECM. Is the replacement complete? | -- | Go to Step 14 | -- |
14 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | Go to Step 15 | -- |
15 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | -- | |
