DTC P0481-High Speed Cooling Fan Relay Circuit fault


Details of the Circuit

  • The cooling fan relay coil receives the Ignition Voltage directly.
  • The relay is regulated by grounding the control circuit via the driver or the internal switch, a process which is entirely controlled by the ECM.
  • The driver has been specially devised to supply the ground for the component being controlled.
  • The ECM monitors the fault line which every driver has.
  • When the ECM is commanding a component ON, the voltage of the control circuit needs to be low (near 0volts).
  • When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high (near battery voltage).
  • The fault line status will automatically change causing the DTC to set if the fault detection circuit senses a voltage different from what is expected.
  • In order to control the high current flow to the cooling fan motors assistance of the relay is sought.
  • This enables the ECM driver to handle the relatively low current used by the relay


Pre-Requisites for Setting the DTC

·   Diagnostic Trouble Codes (DTCs) P0117, P0118 not set.

·   Ignition ON.

·   Ignition voltage is > 10 volts.

·   Engine run time is > 5 seconds.

What happens when DTC sets?

When will DTC clear?

1) The Malfunction Indicator Lamp (MIL) will not glow.


1)A history DTC will clear after 40 consecutive warm-up cycles without a fault

2) The ECM will store conditions which were present when the DTC was set as Failure Records data only.


2) DTC(s) can be cleared by using the scan tool.


3) This information will not be stored in the Freeze Frame data.



Diagnostic Tools

  • An intermittent condition will be located using Freeze Frame and/or failure records data.
  • The information included in the Freeze Frame and/or failure records data can be utilized in calculating how many miles has been covered since the DTC set if the DTC cannot be duplicated.
  • The fail counter and Pass Counter can also be used to determine the number of ignition cycles the diagnostics reported a Freeze Frame conditions (rpm, load, vehicle speed, temperature, etc.) that are noted.
  • This will segregate automatically when the DTC failed.



                                  SUMMARY OF THE STEPS TO BE TAKEN


DTC P0481 - High Speed Cooling Fan Relay Circuit Fault (without A/C)




Task Done? (Yes)

Task Done? (No)


Carry out an EOBD System Check.


Now Follow Step 2

Now Follow "On-Board Diagnostic System Check"


  1. Keeping the engine OFF turn ON the ignition switch
  2. Insert a Scan Tool
  3. Control the relay ON and OFF simultaneously.


Now Follow Step 3

Now Follow Step 5


  1. Turn the ignition switch to LOCK mode.
  2. Dissociate the engine control module (ECM) connector.
  3. Turn the ignition switch to ON.
  4. Measure the current in high speed relay control circuit, at terminal 5 to ground for 2 minutes with the help of a Digital Voltmeter (DVM).

Note: Here the value is 0.75 amps

Does the amperage measure less than the specified value?

Now Follow "Diagnostic Aids"

Now Follow Step 4


  1. Once more turn the ignition switch to LOCK.
  2. Now disconnect the relay.
  3. Measure the resistance between terminals 85 and 5 in the relay control circuit in the ECM harness connector to ground taking the DVM.

Does the DVM display infinite resistance?

Now Follow Step 12

Now Follow Step 10


  1. Turn the ignition switch to LOCK mode.
  2. Detach the relay.
  3. Attach a test light between the relay coil terminals 86 and 85 in the relay harness connector.
  4. Turn ON the ignition switch.
  5. Direct the relay ON and OFF simultaneously by means of a scan tool.


Now Follow Step 8

Now Follow Step 6


With the test light connected to ground, inspect the ignition feed circuit in the relay harness connector.


Now Follow Step 7

Now Follow Step 11


  1. Turn the ignition switch to LOCK mode.
  2. Reconnect the relay.
  3. Disconnect the ECM connector containing the relay control circuit.
  4. Turn ON the ignition switch.
  5. Probe the relay control circuit at terminal 5 in the ECM harness connector with a fused jumper wire connected to ground.


Now Follow Step 9

Now Follow Step 10


Check the connections at the relay.

Do you see any problem?

Now Follow Step 14

Now Follow Step 12


Test the connection at the ECM.


Now Follow Step 11

Now Follow Step 13


Mend the faulty relay control circuit.


Now Follow Step 14



Replace the faulty relay ignition feed circuit.


Now Follow Step 14



Change the relay.


Now Follow Step 14



Replace the ECM.


Now Follow Step 14



  1. Clear the DTCs using the scan tool.
  2. Start the engine and idle at normal operating temperature.
  3. Operate the vehicle within the conditions for setting the DTC as mentioned in the supporting text.

Does the scan tool indicate that this diagnostic was run and passed?

Now Follow Step 15

Now Follow Step 2


Check if any additional DTCs are set.


Do you notice any undiagnosed DTC being displayed?

Now Follow Applicable DTC table

The System of your car is  OK