For 1990-2009 cars

Refer to

#### HVAC Control

Engine Controls Components
Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis
Gen Control, Volts Lamp, Shift Select Switch, EBTCM Module
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
.

### Circuit Description

Power for the cooling fan motors comes from the Cooling Fans Maxi-Fuse. The relays are energized when the PCM grounds the fan relay control circuits. The PCM Output Driver Module (ODM) B output 1 (low speed fan control circuit) is grounded for low speed fan operation. PCM ODM B outputs 1 (low speed fan control circuit) and 2 (high speed fan control circuit) are grounded for High Speed operation. The cooling fan system on this vehicle consists of a single speed right side cooling fan and a dual speed left side cooling fan. While in low speed operation, CKT 409 supplies battery positive voltage directly to the right side cooling fan motor. The left side cooling fan motor is supplied battery positve voltage through a resistor, causing it to run at low speed. When high speed operation is commanded, the right side fan continues to run at low speed. CKT 532 supplies battery positive voltage directly to the left side cooling fan motor, causing it to run at high speed.

The PCM commands low speed fans operation when the following conditions are present:

• | Vehicle speed is less than 58 mph.

• | Engine coolant temperature is greater than 100°C (212°F).

OR

• | Vehicle speed is less than 40 mph.

• | Intake air temperature is greater than 9°C (48°F).

• | A/C refrigerant pressure is greater than 190 psi (1300 kPa).

For high speed cooling fan operation, the PCM delays control of the high speed cooling fan relay for 6 seconds. The 6 second delay ensures that the cooling fan electrical load will not exceed the capacity of the system. High speed fan operation is commanded when the following conditions are present:

• | Vehicle speed is less than 65 mph.

• | Engine coolant temperature is greater than 108°C (226°F).

OR

• | Vehicle speed is less than 50 mph.

• | A/C refrigerant pressure is greater than 260 psi (1800 kPa).

### Diagnostic Aids

Check for the following conditions:

• | Poor connection at the PCM, cooling fan relays, or cooling fan motors.

| 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.

### Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. Stored diagnostic trouble codes may affect engine cooling fan operation. This diagnostic table may lead to improper diagnosis and replacement of good parts if diagnostic trouble codes are present.

2. Ambient temperature must be greater than 9°C (48°F) before the PCM will enable the cooling fans due to A/C request. The PCM will enable the cooling fans if A/C refrigerant pressure increases regardless of ambient temperature.

3. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

#### Electric Cooling Fan Diagnosis

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic(OBD) System Check performed? | -- | Go to Step 2 | Go to the Powertrain On Board Diagnostic (OBD) System Check
2 | Are any PCM DTC(s) stored? | -- | Diagnose the DTCs first - Go to Powertrain Control Module Diagnosis | Go to Step 3
3 |

1. Engine coolant temperature less than 100°C (212°F).
2. Ensure that the A/C is OFF.
3. Engine running.

Observe the cooling fans.

Are the cooling fans running?

--

Go to Step 30

Go to Step 4

4 | Using scan tool output tests command Fan 1 ON. Do both cooling fans run at low speed? | -- | Go to Step 5 | Go to Step 8
5 | Using scan tool output tests command Fan 2 ON. Does the left side cooling fan run at high speed? | -- | Go to Step 6 | Go to Step 18
6 | Important: Ambient temperature must be greater than 9°C (48°F).

1. Exit scan tool output tests.
2. Engine running.
3. Turn the A/C ON.

Are the cooling fans running?

--

Go to Diagnostic Aids

Go to Step 7

7 | View the A/C Request display on the scan tool. Does the scan tool display Yes? | -- | Go to Step 44 | Go to Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis
8 |

1. Turn OFF the ignition switch.
2. Disconnect the low speed cooling fan relay.
3. Turn ON the ignition switch.
4. Probe low speed cooling fan relay harness connector terminal 85 with a test light connected to ground

Is the test light ON?

--

Go to Step 9

Go to Step 28

9 | Probe low speed cooling fan relay harness connector terminal 30 with a test light to ground. Is the test light ON? | -- | Go to Step 10 | Go to Step 29
10 |

1. Connect a fused jumper between low speed cooling fan relay harness connector terminals 87 and 30.
2. Observe the cooling fans.

Are both cooling fans running at low speed?

--

Go to Step 11

Go to Step 14

11 |

1. Using the scan tool output control function, select Fan 1 and command the cooling fans ON.
2. Probe low speed cooling fan harness connector terminal 86 with a test light to B+.

Is the test light ON?

--

Go to Step 40

Go to Step 12

12 |

1. Turn OFF the ignition switch.
2. Disconnect the PCM.
3. Turn ON the ignition switch.
4. Check the low speed cooling fan relay control circuit for an open or short to voltage between the PCM and the low speed cooling fan relay.
5. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 46

Go to Step 13

13 |

1. Check the low speed cooling fan relay control circuit for a poor terminal connection at the PCM.
2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 46

Go to Step 44

14 |

1. Disconnect both cooling fan motor 2-way harness connectors (leave low speed cooling fan relay connector terminals 87 and 30 jumpered).
2. Probe terminal B at both cooling fan motor connectors with a test light to ground.

Is the test light ON at both cooling fan connectors?

--

Go to Step 15

Go to Step 16

15 | Connect the test light between terminals A and B at both cooling fan connectors. Is the test light ON at both cooling fan connectors? | -- | Go to Step 45 | Go to Step 17
16 | Locate and repair open in CKT 409 to the affected cooling fan motor(s). Is action complete? | -- | Go to Step 46 | --
17 | Locate and repair open in the ground circuit to the affected cooling fan motor(s). Is action complete? | -- | Go to Step 46 | --
18 |

1. Disconnect the high speed cooling fan relay
2. Turn ON the ignition switch.
3. Probe high speed cooling fan relay harness connector terminal 30 with a test light to ground.

Is the test light ON?

--

Go to Step 19

Go to Step 29

19 | Probe high speed cooling fan relay harness connector terminal 86 with a test light to ground. Is the test light ON? | -- | Go to Step 20 | Go to Step 28
20 |

1. Connect a fused jumper between high speed cooling fan relay harness connector terminals 30 and 87.
2. Observe the left side cooling fan.

Does the left side cooling fan run at high speed?

--

Go to Step 21

Go to Step 24

21 |

1. Using the scan tool output control function, select Fan 2 and command the fan ON.
2. Wait 6 seconds.
3. Probe high speed cooling fan harness connector terminal 86 with a test light to B+.

Is the test light ON?

--

Go to Step 42

Go to Step 22

22 |

1. Turn OFF the ignition switch.
2. Disconnect the PCM.
3. Turn ON the ignition switch.
4. Check the high speed cooling fan relay control circuit for an open or short to voltage between the PCM and the high speed cooling fan relay.
5. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 46

Go to Step 23

23 |

1. Check the high speed cooling fan relay control circuit for a poor terminal connection at the PCM.
2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 46

Go to Step 44

24 |

1. Disconnect the left side cooling fan motor connector (leave high speed cooling fan relay harness connector terminals 30 and 87 jumpered).
2. Probe the left side cooling fan motor harness connector terminal B with a test light to ground.

Is the test light ON?

--

Go to Step 25

Go to Step 27

25 | Connect the test light between left side cooling fan motor harness connector terminals A and B. Is the test light ON? | -- | Go to Step 45 | Go to Step 26
26 | Locate and repair open in the ground circuit to the left side cooling fan motor. Is action complete? | -- | Go to Step 46 | --
27 | Locate and repair open in CKT 532 to the left side cooling fan. Is action complete? | -- | Go to Step 46 | --
28 | Locate and repair open in ignition feed (CKT 241) to the affected cooling fan relay. Is action complete? | -- | Go to Step 46 | --
29 | Locate and repair cause of no battery feed to the affected fan relay cavity 30:

• | Open or short to ground in CKT 742.

• | Shorted cooling fan motor windings.

• | CKT 409 shorted to ground.

• | CKT 532 shorted to ground.

Is action complete?

--

Go to Step 46

--

30 | Disconnect the high speed cooling fan relay. Is either cooling fan running? | -- | Go to Step 35 | Go to Step 31
31 | Probe the high speed cooling fan relay harness connector terminal 86 with a test light to B+. Is the test light ON? | -- | Go to Step 32 | Go to Step 43
32 | Observe A/C High Side Pressure on the scan tool. Is A/C High Side Pressure greater than the specified value? | 260 psi (1800 kPa) | Go to Diagnosis in Heater Ventilation and Air Conditioning | Go to Step 33
33 |

1. Turn OFF the ignition switch.
2. Disconnect the PCM.
3. Turn ON the ignition switch.
4. Probe the high speed cooling fan relay harness connector terminal 86 with a test light to B+.

Is the test light ON?

--

Go to Step 34

Go to Step 44

34 | Locate and repair the short to ground in the high speed cooling fan relay control circuit. Is action complete? | -- | Go to Step 46 | --
35 | Disconnect the low speed cooling fan relay. Is either cooling fan ON? | -- | Go to Step 39 | Go to Step 36
36 | Probe the low speed cooling fan relay harness connector terminal 86 with a test light to B+. Is the test light ON? | -- | Go to Step 37 | Go to Step 41
37 |

1. Turn OFF the ignition switch.
2. Disconnect the PCM.
3. Turn ON the ignition switch.
4. Probe the low speed cooling fan relay harness connector terminal 86 with a test light to B+.

Is the test light ON?

--

Go to Step 38

Go to Step 44

38 | Locate and repair the short to ground in the low speed cooling fan relay control circuit. Is action complete? | -- | Go to Step 46 | --
39 | Locate and repair short to B+ in affected cooling fan feed CKT 409 or CKT 532. Is action complete? | -- | Go to Step 46 | --
40 |

1. Check for poor connections at the low speed cooling fan relay.
2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 46

Go to Step 41

41 | Replace the low speed cooling fan relay. Is action complete? | -- | Go to Step 46 | --
42 |

1. Check for poor connections at the high speed cooling fan relay.
2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 46

Go to Step 43

43 | Replace the high speed cooling fan relay. Is action complete? | -- | Go to Step 46 | --
44 | Replace the PCM. Important: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | Go to Step 46 | --
45 | Replace the affected cooling fan motor. Refer to On-Vehicle Service in Cooling and Radiator. Is action complete? | -- | Go to Step 46 | --
46 |

1. Engine coolant temperature is less than 100°C (212°F).
2. Ensure that the A/C is OFF.
3. Engine running.

Are the cooling fans running?

--

Go to Step 30

Go to Step 47

47 | Using scan tool output tests command Fan 1 ON. Do both cooling fans run at low speed? | -- | Go to Step 48 | Go to Step 8
48 | Using scan tool output tests command Fan 2 ON. Does the left side cooling fan run at high speed? | -- | System OK | Go to Step 18