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 to 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 DTC:
DTC P0481 Cooling Fan Relay 2 Control Circuit
Conditions for Running the DTC
| • | The ignition is ON. |
| • | DTC P0481 runs continuously when the above condition is met. |
Conditions for Setting the DTC
The high speed cooling fan control circuit is an open, or a short to battery to or a short to ground condition exists.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The ECM will store conditions which were present when the DTC was set as Failure Records data only. |
| • | This information will not be stored in the Freeze Frame data. |
Conditions for Clearing the MIL/DTC
| • | A history DTC will clear after 40 consecutive warm-up cycles 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 Freeze Frame conditions, such as RPM, load, vehicle speed, temperature, etc., that are noted. This will isolate when the DTC failed.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Perform the Diagnostic System Check-Engine Controls. Is the system check complete? | -- | Go to Step 2 | |
2 |
Does the relay turn ON and OFF when commanded? | -- | Go to Step 3 | Go to Step 5 |
3 |
Does the amperage measure less than the specified value? | 0.75 A | 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 | With the test light connected to ground, probe the ignition feed circuit in the relay harness connector. Does the test light illuminate? | -- | Go to Step 7 | Go to Step 11 |
7 |
Does the relay operate? | -- | Go to Step 9 | Go to Step 10 |
8 | Inspect the connections at the relay. Is a condition found and corrected? | -- | Go to Step 14 | Go to Step 12 |
9 | Inspect the connection at the ECM. Is a condition 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. Refer to Engine Control Module Replacement . Is the replacement complete? | -- | Go to Step 14 | -- |
14 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | Go to Step 15 | Go to Step 2 |
15 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | System OK |
