GM Service Manual Online
For 1990-2009 cars only

Refer to

Cooling Fans Controls


Object Number: 378500  Size: FS
Cell 10: Underhood Accessory Wiring Junction Block
Cell 14: L36 Engine Ground G117
Cell 14: L36 Engine Ground G117
A/C Compressor Controls
OBD II Symbol Description Notice
Engine Controls Components
Handling ESD Sensitive Parts Notice

Circuit Description

Output Driver Modules (ODMs) are used by the PCM to turn on many of the current-driven devices that are needed to control various engine and Transaxle functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the device which the PCM is commanding ON. Unlike the Quad Driver Modules (QDMs) used in prior model years, ODMs have the capability of diagnosing each output circuit individually. DTC P1651 set indicates an improper voltage level has been detected on the output circuit which controls the low speed cooling fans relay.

Conditions for Setting the DTC

    • The ignition is ON.
    • An improper voltage level has been detected on the output circuit which controls the fan 1 relay.
    • The above conditions present for at least 30 seconds.

Action Taken When the DTC Sets

    • The PCM will illuminate the MIL during the second consecutive trip in which the diagnostic test has been run and failed.
    • The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC

    • The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.
    • The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
    • The DTC can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.

Diagnostic Aids

Check for the following conditions:

    • Poor connection at the PCM.
        Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
    • Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM, turn the ignition ON and observe a voltmeter connected between the Fan 1 control circuit and ground at the PCM harness connector while moving connectors and wiring harnesses related to the Fan 1 relay. A change in voltage will indicate the location of the malfunction.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description

The number(s) below refer to the step number(s) on the Diagnostic Chart.

  1. This vehicle is equipped with a powertrain control module (PCM) which utilizes an electrically erasable programmable read-only memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.

DTC P1651 - Fan 1 Relay Control Circuit

Step

Action

Value(s)

Yes

No

1

Did you perform the On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Turn the ignition switch to the OFF position.
  2. Disconnect the PCM connector.
  3. Turn the ignition switch to the ON position.
  4. Use a digital multimeter (DMM) in order to measure the voltage between the low speed fans control circuit and ground.

Is the voltage near the specified value?

B+

Go to Step 3

Go to Step 6

3

  1. Turn the ignition switch to the OFF position.
  2. Leave the PCM disconnected.
  3. Remove the cool fan 1 relay.
  4. Turn the ignition switch to the ON position.
  5. Use the DMM in order to measure the voltage between the low speed fans control circuit and ground.

Is the voltage near the specified value?

0 V

Go to Step 4

Go to Step 5

4

  1. Turn the ignition switch to the OFF position.
  2. Leave the PCM disconnected.
  3. Reinstall the cool fan 1 relay.
  4. Set the DMM to the 10 amp scale.
  5. Turn the ignition switch to the ON position.
  6. Measure the current between the low speed fans control circuit and ground.
  7. Monitor the current reading on the DMM for a least 2 minutes.

Is the current reading within the specified range?

0.05-1.5 amps

Go to Step 12

Go to Step 14

5

Locate and repair the short to voltage in the low speed fans control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step  16

--

6

  1. Leave the PCM disconnected.
  2. Test the battery positive feed fuse for the cool fan 1 relay

Is the fuse open?

--

Go to Step 7

Go to Step 8

7

Locate and repair the short to voltage in the battery positive feed circuit to the cool fan 1 relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step  16

--

8

  1. Leave the PCM disconnected.
  2. Turn the ignition switch to the OFF position.
  3. Remove the cool fan 1 relay.
  4. Turn the ignition switch to the ON position.
  5. Connect the test lamp to ground.
  6. Probe the battery positive feed cavity for the cool fan 1 relay.

Does the test lamp illuminate?

--

Go to Step  9

Go to Step  11

9

  1. Leave the PCM disconnected.
  2. Leave the cool fan 1 relay disconnected.
  3. Test the low speed fans control circuit for an open or short to ground.
  4. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step  16

Go to Step  10

10

  1. Leave the PCM disconnected.
  2. Leave the cool fan 1 relay disconnected.
  3. Test he low speed fans control circuit for faulty terminal connections at the PCM and the relay connector.
  4. If a problem is found, repair as necessary. Refer to Connector Repairs in Wiring Systems.

Was a problem found?

--

Go to Step  16

Go to Step  15

11

  1. Locate and repair the following circuit conditions:
  2. • An open in the battery positive feed circuit to cool fan 1 relay.
    • Any faulty connections between the battery positive feed fuse and the fuse block.
  3. Refer to Repair Procedures in Wiring Repairs or to Connector Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step  16

--

12

  1. Turn the ignition switch to the OFF position.
  2. Remove the cool fan 1 relay.
  3. Reconnect the PCM connector.
  4. Turn the ignition switch to the ON position.
  5. Use the proper jumpers in order to connect the test lamp between the battery positive feed and the low speed fans control circuit in the cool fan 1 relay connector.
  6. Use the scan tool ouputs functions in order to cycle the cool fan 1 relay on and off.

Does the test lamp flash?

--

Go to Diagnostic Aids

Go to Step 13

13

  1. Test the low speed fans control circuit for a faulty connection at the PCM.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Step  16

Go to Step  15

14

Replace the cool fan 1 relay.

Did you complete the repair?

--

Go to Step  16

--

15

Important: Replacement PCM must be reprogrammed. Powertrain Control Module Replacement/Programming .

Replace the PCM.

Did you complete the repair?

--

Go to Step  16

--

16

  1. Review and record the scan tool Fail Records data.
  2. Clear the DTCs
  3. Operate the vehicle within the Fail Records conditions as noted.
  4. Use the scan tool in order to monitor the Specific DTC info for DTC P1651.

Does the scan tool indicate that DTC P1651 Failed This Ign?

--

Go to Step 2

System OK