Circuit Description
Power for the cooling fan motors comes from the Cool Fan 1 and Cool Fan 2 Maxi fuses®. 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 two speed dual speed cooling fans. 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 the right side cooling fan motor, causing both cooling fans to run at low speed. When high speed operation is commanded, the right side fan and left side fans are supplied with their own battery positive voltage feed and ground, causing both cooling fans 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 fans operation. This diagnostic table may lead to improper diagnosis and replacement of good parts if diagnostic trouble codes are present.
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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 powertrain DTC(s) stored? | -- | Diagnose the DTC(s) first. Go to Powertrain Control Module Diagnosis | ||||||||||||
3 |
Are the cooling fan(s) running? | -- | ||||||||||||
4 |
Are both cooling fans running at low speed? | -- | ||||||||||||
5 |
Are both fans running at high speed? | -- | ||||||||||||
|
Important:: Ambient temperature must be greater than 9°C (48°F).
Are the cooling fans running? | -- | Refer to Diagnostic Aids | ||||||||||||
7 | View A/C Request on the scan tool. Does A/C Request on the scan tool display Yes? | -- | Go to A/C Controls Diagnosis in Heater, Ventilation, and Air Conditioning | |||||||||||
8 | Is either cooling fan running? | -- | ||||||||||||
9 | Is the LH cooling fan running? | -- | ||||||||||||
10 |
Is the LH cooling fan running? | -- | ||||||||||||
11 | Remove the series/parallel cooling fan relay from the underhood Bussed Electrical Center. Is the LH cooling fan running? | -- | ||||||||||||
12 | Locate and repair short to ground in CKT 504. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
13 |
Was a problem found? | -- | ||||||||||||
14 |
Is the RH cooling fan running? | -- | ||||||||||||
15 | Replace the LH cooling fan diode. Refer to Cooling Fans in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
16 |
Is the test light ON? | -- | ||||||||||||
17 |
Is action complete? | -- | -- | |||||||||||
18 | Probe low speed cooling fan relay #2 harness connector cavity 85 with a test light connected to ground. Is the test light ON? | -- | ||||||||||||
19 |
Is action complete? | -- | -- | |||||||||||
20 |
Is the test light ON? | -- | ||||||||||||
21 |
Is the test light ON? | -- | ||||||||||||
22 |
Are both cooling fans running? | -- | ||||||||||||
23 |
Was a problem found? | -- | ||||||||||||
24 |
Was a problem found? | -- | ||||||||||||
25 |
Is the test light ON? | -- | ||||||||||||
26 | Repair open in the low speed fans control CKT 335 between the PCM and the low speed cooling fan relay #2. Is action complete? | -- | -- | |||||||||||
27 |
Is the test light ON? | -- | ||||||||||||
28 | Connect a test light between Underhood Bussed Electrical Center series/parallel cooling fan relay cavities 30 and 87A. Is the test light ON? | -- | ||||||||||||
29 |
Was a problem found? | -- | ||||||||||||
30 |
Was a problem found? | -- | ||||||||||||
31 |
Was a problem found? | -- | ||||||||||||
32 | Using scan tool, view A/C Request. Does the scan tool display Yes? | -- | Go to A/C Controls Diagnosis in Heater, Ventilation, And Air Conditioning | |||||||||||
33 | Are both cooling fan(s) running at low speed? | -- | ||||||||||||
34 | Disconnect the low speed cooling fan relay #2. Are the cooling fans running? | -- | ||||||||||||
35 | Locate and repair short to voltage in CKT 532. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
36 | Using a test light connected to B+, probe low speed cooling fan relay #2 harness connector cavity 85. Is the test light ON? | -- | ||||||||||||
37 | Replace the low speed cooling fan relay #2. Is action complete? | -- | -- | |||||||||||
38 |
Is the test light ON? | -- | ||||||||||||
39 | Locate and repair short to ground in the low speed cooling fan control circuit (CKT 335). Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
40 | Are both cooling fans running at high speed? | -- | ||||||||||||
41 | View A/C High Side Pressure on the scan tool. Does the scan tool display voltage less than the specified value? | 1.2V | ||||||||||||
42 |
Is the RH cooling fan running at high speed? | -- | ||||||||||||
43 |
Was a problem found? | -- | ||||||||||||
44 |
Does the scan tool display voltage near the specified value? | 0V | ||||||||||||
45 | Probe the A/C refrigerant pressure signal circuit with a J 39200 Digital Multimeter connected to the A/C refrigerant pressure sensor ground. Does the digital multimeter display voltage near the specified value? | 0V | ||||||||||||
46 | Probe the A/C refrigerant pressure sensor ground circuit with a test light to B+. Is the test light ON? | -- | ||||||||||||
47 | Probe the A/C refrigerant pressure sensor 5 volt reference circuit B with a J 39200 Digital Multimeter connected to the A/C refrigerant pressure sensor ground. Does the digital multimeter display voltage near the specified value? | 5V | ||||||||||||
48 | Replace the A/C refrigerant pressure sensor. Refer to On-Vehicle Service in Heater, Ventilation, and Air Conditioning. Is action complete? | -- | -- | |||||||||||
49 | Locate and repair open or short to voltage in the A/C refrigerant pressure sensor ground circuit. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
50 | Locate and repair open or short to ground in the A/C refrigerant pressure sensor 5 volt reference B circuit. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
51 | Locate and repair short to voltage in the A/C refrigerant pressure signal circuit. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
52 |
Is the RH cooling fan running at high speed? | -- | ||||||||||||
53 | Remove the series/parallel cooling fan relay from the underhood Bussed Electrical Center. Is the RH cooling fan running at high speed? | -- | ||||||||||||
54 | Locate and repair short to B+ in CKT 409. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
55 | Locate and repair short to B+ in CKT 504. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
56 |
Was a problem found? | -- | ||||||||||||
57 |
Was a problem found? | -- | ||||||||||||
58 |
Is the test light ON? | -- | ||||||||||||
59 |
Is the test light ON? | -- | ||||||||||||
60 |
Was a problem found? | -- | ||||||||||||
61 |
Is the test light ON? | -- | ||||||||||||
62 | Probe terminal A (CKT 504) at the LH cooling fan connector with a test light to B+. Is the test light ON? | -- | ||||||||||||
63 |
Is action complete? | -- | -- | |||||||||||
64 |
Is the test light ON? | -- | ||||||||||||
65 | Locate and repair open in the battery positive voltage circuit to high speed cooling fan relay #1. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
66 | Probe high speed cooling fan relay #1 cavity 30 in the Underhood Bussed Electrical Center with a test light connected to ground. Is the test light ON? | -- | ||||||||||||
67 | Locate and repair open in battery positive voltage circuit to high speed cooling fan relay #1 cavity 30. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
68 |
Was a problem found? | -- | ||||||||||||
69 |
Was a problem found? | -- | ||||||||||||
70 | Replace the high speed cooling fan relay #1. Is action complete? | -- | -- | |||||||||||
71 |
Is the test light ON? | -- | ||||||||||||
72 | Locate and repair open in battery positive voltage circuit to series/parallel cooling fan relay cavity 85 in the Underhood Bussed Electrical Center. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
73 | Probe series/parallel cooling fan relay cavity 30 in the Underhood Bussed Electrical Center with a test light to B+. Is the test light ON? | -- | ||||||||||||
74 | Locate and repair open in CKT 1250 between series/parallel cooling fan relay cavity 87 in the Underhood Bussed Electrical Center cavity and ground. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
75 |
Was a problem found? | -- | ||||||||||||
76 | Replace the series/parallel 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? | -- | -- | ||||||||||||
78 | Repair open in the high speed cooling fans control circuit (CKT 473) to high speed cooling fan relay #1 cavity 86. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |||||||||||
79 | Replace the LH cooling fan motor. Refer to On-Vehicle Service in Cooling and Radiator. Is action complete? | -- | -- | |||||||||||
80 | Replace the RH cooling fan motor. Refer to On-Vehicle Service in Cooling and Radiator. Is action complete? | |||||||||||||
81 |
Observe the cooling fans. Are the cooling fans running? | -- | ||||||||||||
82 |
Are both cooling fans running at low speed? | -- | ||||||||||||
83 |
Are both cooling fans running at high speed? | -- | System OK |
