Circuit Description:
The electric cooling fan(s) are controlled by the Body Function Controller (BFC) which enables the fans through the PCM. The PCM enables the ground path for the three cooling fan relays. The relay(s) are used to control the high current flow to power the cooling fan motors. When minimum cooling is required, the BFC will command the PCM to energize cooling fan relay #1 and since both fans are connected in series through the Mode Control relay, both fans will operate at low speed. When maximum cooling is required, the BFC will command the PCM to energize all three cooling fan relays. Power is supplied to the left fan through the Mode Control relay. The right fan is powered directly through cooling fan relay #2 causing both fans to operate at high speed.
Diagnostic Aids
If the owner complained of an overheating problem, determine if the complaint was due to an actual boil over, or the warning indicator illuminated, or the engine coolant temperature gauge indicated overheating. The gauge accuracy can also be checked by comparing the ECT Sensor reading using a scan tool and comparing its reading with the gauge reading. If the engine is actually overheating and the gauge indicated overheating, but the cooling fan(s) are turning on, the ECT sensor may have shifted out of calibration and should be replaced. If the engine is overheating and the cooling fans are on, the cooling system is suspect and should be checked. Refer to Engine Overheating in Engine Mechanical.
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. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs and Wiring Repairs in Wiring Systems. |
| • | Damaged harness. Inspect the wiring harness for damage. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs and Wiring Repairs in Wiring Systems. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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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 above 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.
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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. Refer to Powertrain Control Module Replacement/Programming .
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain ON Board Diagnostic (OBD) System Check performed? | -- | ||||||||||||
Are any PCM DTCs stored? | -- | Diagnose the PCM DTCs first | ||||||||||||
3 |
Are the cooling fans running? | -- | ||||||||||||
4 |
Are both cooling fans running at low speed? | -- | ||||||||||||
5 |
Are both fans running at high speed? | -- | ||||||||||||
|
Important: Ambient temperature must be above 9°C (48°F).
Are the cooling fans ON? | -- | Go to Diagnostic Aids | ||||||||||||
7 | View A/C Request on the scan tool. Does A/C Request on the scan tool display Yes? | -- | Go to Air Conditioning (A/C) Compressor Control Circuit Diagnosis | |||||||||||
8 | Is either cooling fan running? | -- | ||||||||||||
9 | Is the left cooling fan running? | -- | ||||||||||||
10 |
Is the left engine cooling fan running? | -- | ||||||||||||
11 | Remove the Mode control relay (cool fan series) from the U/H BEC. Is the left engine cooling fan running? | -- | ||||||||||||
12 | Locate and repair short to ground in CKT 504. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||
13 |
Was a problem found? | -- | ||||||||||||
14 |
Is the right engine cooling fan running? | -- | ||||||||||||
15 |
Was a problem found? | -- | ||||||||||||
16 |
Is the test light ON? | -- | ||||||||||||
17 |
Is the action complete? | -- | -- | |||||||||||
18 | Probe #1 Fan Control Relay cavity 86 with a test light connected to ground. Is the test light ON? | -- | ||||||||||||
19 |
Is the 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 | Locate and repair open in the relay control circuit between the PCM and #1 Fan Control Relay cavity 86. Is the action complete? | -- | -- | |||||||||||
27 |
Is the test light ON? | -- | ||||||||||||
28 | Connect a test light between Mode control relay (cool fan series) in U/H BEC 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 Air Conditioning (A/C) Compressor Control Circuit Diagnosis | |||||||||||
33 | Are both cooling fans running at low speed? | -- | ||||||||||||
34 | Remove #1 Fan Control Relay from the U/H BEC. Are the cooling fans running? | -- | ||||||||||||
35 | Locate and repair short to voltage in CKT 409. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||
36 | Using a test light connected to battery positive voltage, probe #1 Fan Control Relay cavity 86. Is the test light ON? | -- | ||||||||||||
37 | Replace #1 Fan Control Relay. Is the action complete? | -- | -- | |||||||||||
38 |
Is the test light ON? | -- | ||||||||||||
39 | Locate and repair short to ground in the #1 Fan Control Relay control circuit. Refer to Repair Procedures in Electrical Diagnosis. Is the action complete? | -- | -- | |||||||||||
40 | Are both cooling fans running at high speed? | -- | ||||||||||||
41 | View A/C Pressure on the scan tool. Does the scan tool display voltage less than the specified value? | 1.2V | ||||||||||||
42 |
Is the right engine cooling fan running at high speed? | -- | ||||||||||||
43 |
Was a problem found? | -- | ||||||||||||
44 |
Does the scan tool display voltage near the specified value? | 0.0V | ||||||||||||
45 | Probe the A/C refrigerant pressure signal circuit with a J 39200 DMM. Does the digital multimeter display voltage near the specified value? | 0.0V | ||||||||||||
46 | Probe the A/C refrigerant pressure sensor ground with a test light to battery positive voltage. Is the test light ON? | -- | ||||||||||||
47 | Probe the A/C refrigerant pressure sensor 5 volt reference circuit with a J 39200 DMM. Does the digital multimeter display voltage near the specified value? | 5.0V | ||||||||||||
48 | Replace the A/C refrigerant pressure sensor. Refer to On-Vehicle Service in Heater, Ventilation, and Air Conditioning. Is the action complete? | -- | -- | |||||||||||
49 | Locate and repair open or short to voltage in the A/C refrigerant pressure sensor ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||
50 | Locate and repair open or short to ground in the A/C refrigerant pressure sensor 5 volt reference circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||
51 | Locate and repair short to voltage in the A/C refrigerant pressure signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||
52 |
Is the right engine cooling fan running at high speed? | -- | ||||||||||||
53 | Remove the #2 Fan Control Relay from the U/H BEC. Is the right engine cooling fan running at high speed? | -- | ||||||||||||
54 | Locate and repair short to battery positive voltage in CKT 532. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||
55 |
Was a problem found? | -- | ||||||||||||
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 at the left engine cooling fan connector with a test light to battery positive voltage. Is the test light ON? | -- | ||||||||||||
63 |
Is the action complete? | -- | -- | |||||||||||
64 |
Is the test light ON? | -- | ||||||||||||
65 | Locate and repair open in the battery positive voltage circuit to Mode control relay (cool fan series). Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||
66 | Probe Mode control relay (cool fan series) cavity 30 with a test light connected to ground. Is the test light ON? | -- | ||||||||||||
67 | Locate and repair open in battery positive voltage circuit to Mode control relay (cool fan series) cavity 30. Refer to Repair Procedures in Electrical Diagnosis. Is the action complete? | -- | -- | |||||||||||
68 |
Was a problem found? | -- | ||||||||||||
69 |
Was a problem found? | -- | ||||||||||||
70 | Replace Mode control relay (cool fan series). Is the action complete? | -- | -- | |||||||||||
71 |
Is the test light ON? | -- | ||||||||||||
72 | Locate and repair open in battery positive voltage circuit to #2 Fan Control Relay cavity 86. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||
73 | Probe #2 Fan Control Relay cavity 87 in the U/H BEC with a test light to battery positive voltage. Is the test light ON? | -- | ||||||||||||
74 | Locate and repair open in circuit between #2 Fan Control Relay cavity 87 and Mode control relay (cool fan series) cavity 87A in the U/H BEC and ground. Refer to Repair Procedures in Electrical Diagnosis. Is the action complete? | -- | -- | |||||||||||
75 |
Was a problem found? | -- | ||||||||||||
76 | Replace the #2 Fan Control Relay in the U/H BEC. Is the action complete? | -- | -- | |||||||||||
|
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming Replace the PCM. Is the action complete? | -- | -- | ||||||||||||
78 | Repair open in the Mode control relay (cool fan series) cavity 85 and #2 Fan Control Relay cavity 86 control circuit to PCM. Refer to Repair Procedures in Electrical Diagnosis. Is the action complete? | -- | -- | |||||||||||
79 | Replace the Left Hand Engine Cooling Fan motor. Refer to ON Vehicle Service in Cooling and Radiator. Is the action complete? | -- | -- | |||||||||||
80 | Replace the Right Hand Engine Cooling Fan motor. Refer to ON-Vehicle Service in Cooling and Radiator. Is the 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 |
