Refer to
HVAC Control
.
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.
-
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.
-
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.
-
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.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic(OBD) System Check performed? | -- | ||||||||||
Are any PCM DTC(s) stored? | -- | Diagnose the DTCs first - Go to Powertrain Control Module Diagnosis | ||||||||||
3 |
Observe the cooling fans. Are the cooling fans running? | -- | ||||||||||
4 | Using scan tool output tests command Fan 1 ON. Do both cooling fans run at low speed? | -- | ||||||||||
5 | Using scan tool output tests command Fan 2 ON. Does the left side cooling fan run at high speed? | -- | ||||||||||
|
Important: Ambient temperature must be greater than 9°C (48°F).
Are the cooling fans running? | -- | Go to Diagnostic Aids | ||||||||||
7 | View the A/C Request display on the scan tool. Does the scan tool display Yes? | -- | Go to Powertrain Control Module Controlled Air Conditioning (A/C) Circuit Diagnosis | |||||||||
8 |
Is the test light ON? | -- | ||||||||||
9 | Probe low speed cooling fan relay harness connector terminal 30 with a test light to ground. Is the test light ON? | -- | ||||||||||
10 |
Are both cooling fans running at low speed? | -- | ||||||||||
11 |
Is the test light ON? | -- | ||||||||||
12 |
Was a problem found? | -- | ||||||||||
13 |
Was a problem found? | -- | ||||||||||
14 |
Is the test light ON at both cooling fan connectors? | -- | ||||||||||
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? | -- | ||||||||||
16 | Locate and repair open in CKT 409 to the affected cooling fan motor(s). Is action complete? | -- | -- | |||||||||
17 | Locate and repair open in the ground circuit to the affected cooling fan motor(s). Is action complete? | -- | -- | |||||||||
18 |
Is the test light ON? | -- | ||||||||||
19 | Probe high speed cooling fan relay harness connector terminal 86 with a test light to ground. Is the test light ON? | -- | ||||||||||
20 |
Does the left side cooling fan run at high speed? | -- | ||||||||||
21 |
Is the test light ON? | -- | ||||||||||
22 |
Was a problem found? | -- | ||||||||||
23 |
Was a problem found? | -- | ||||||||||
24 |
Is the test light ON? | -- | ||||||||||
25 | Connect the test light between left side cooling fan motor harness connector terminals A and B. Is the test light ON? | -- | ||||||||||
26 | Locate and repair open in the ground circuit to the left side cooling fan motor. Is action complete? | -- | -- | |||||||||
27 | Locate and repair open in CKT 532 to the left side cooling fan. Is action complete? | -- | -- | |||||||||
28 | Locate and repair open in ignition feed (CKT 241) to the affected cooling fan relay. Is action complete? | -- | -- | |||||||||
29 | Locate and repair cause of no battery feed to the affected fan relay cavity 30:
Is action complete? | -- | -- | |||||||||
30 | Disconnect the high speed cooling fan relay. Is either cooling fan running? | -- | ||||||||||
31 | Probe the high speed cooling fan relay harness connector terminal 86 with a test light to B+. Is the test light ON? | -- | ||||||||||
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 | |||||||||
33 |
Is the test light ON? | -- | ||||||||||
34 | Locate and repair the short to ground in the high speed cooling fan relay control circuit. Is action complete? | -- | -- | |||||||||
35 | Disconnect the low speed cooling fan relay. Is either cooling fan ON? | -- | ||||||||||
36 | Probe the low speed cooling fan relay harness connector terminal 86 with a test light to B+. Is the test light ON? | -- | ||||||||||
37 |
Is the test light ON? | -- | ||||||||||
38 | Locate and repair the short to ground in the low speed cooling fan relay control circuit. Is action complete? | -- | -- | |||||||||
39 | Locate and repair short to B+ in affected cooling fan feed CKT 409 or CKT 532. Is action complete? | -- | -- | |||||||||
40 |
Was a problem found? | -- | ||||||||||
41 | Replace the low speed cooling fan relay. Is action complete? | -- | -- | |||||||||
42 |
Was a problem found? | -- | ||||||||||
43 | Replace the high speed cooling fan relay. Is action complete? | -- | -- | |||||||||
Replace the PCM. Important: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||||||||||
45 | Replace the affected cooling fan motor. Refer to On-Vehicle Service in Cooling and Radiator. Is action complete? | -- | -- | |||||||||
46 |
Are the cooling fans running? | -- | ||||||||||
47 | Using scan tool output tests command Fan 1 ON. Do both cooling fans run at low speed? | -- | ||||||||||
48 | Using scan tool output tests command Fan 2 ON. Does the left side cooling fan run at high speed? | -- | System OK |
