APPLICATION
| Application | Engine |
|---|---|
| "L" Body | 2.0L & 2.8L |
ELECTRIC COOLING FAN APPLICATIONS
Note. This article contains test charts that are part of General Motors Computerized Engine Controls. Only those charts required to test electric cooling fans are included. Other diagnostic codes may appear while performing electric cooling fan diagnosis. For complete information on General Motors Computerized Engine Control systems see COMPUTERIZED ENGINE CONTROL section.
DESCRIPTION
All FWD, and some RWD vehicles use an electric cooling fan. This fan is used for engine and A/C condenser cooling and operates when A/C is on and if engine overheats.
OPERATION
All electric cooling fans operate when engine coolant temperature exceeds a certain value. The ECM completes ground path for the cooling fan relay. Relay contacts then close and complete circuit between fusible link and fan motor. When the engine cools, the switch opens and fan stops. If coolant sensor fails, the ECM will command constant fan operation.
A/C equipped vehicles have a separate signal line to the ECM for fan control. When A/C control switch is "ON", and A/C system low pressure switch is closed, the ECM receives a signal on this line and turns on the cooling fan. The compressor clutch does not have to engage for ECM to turn fan on.
On some models, when engine is off, ECM may turn on the fan relay and run fan for up to 7 minutes. This occurs if hot conditions were present while engine was running. Hot conditions are based on Manifold Absolute Temperature (MAT) signal to ECM, coolant temperature and time from start.
Battery voltage is supplied to fan relay circuit No. 2 and from ignition switch to circuit No. 39. Grounding relay circuit No. 335 will close relay and supply battery voltage to fan motor. When engine is running, the ECM will turn the cooling fan on if
- A/C is on.
- Coolant temperature is greater than 226°F (108°C).
- Code 14 or 15 is set.
Diagnostic Aids
If an overheating condition is suspected, verify if this is due to actual boil over. If gauge or light indicates an overheat condition, and no boil over is in evidence, inspect the gauge/light circuit for malfunction.
If vehicle is overheating and the gauge or light indicates the same, but the cooling fan is not coming on, check coolant sensor temperature using a "SCAN" tester. Sensor may have shifted calibration. If engine is overheating and cooling fan is on, check cooling system.
The cooling fan is controlled by the ECM based on inputs from the coolant sensor and fan control switch. The fan should run if coolant temperature is more than 223°F (106°C). Battery voltage is supplied to the fan relay on circuit No. 2 (relay terminal "A") and ignition voltage to circuit No. 250.
Grounding circuit No. 335 (relay terminal "F") will energize the relay and supply battery voltage to the fan motor. Once the fan relay is energized by the ECM, it will remain on for a minimum of 30 seconds.
The fan control switch mounted, in the A/C high pressure line, will open when head pressure exceeds 200 psi (14 kg/cm 2 ). This input causes the ECM to ground circuit No. 335. If a Code 14 or 15 sets or the ECM is operating in the fuel back-up mode the ECM will turn on the cooling fan.
Note. Test numbers refer to test numbers on diagnostic charts.
- With diagnostic terminal grounded, cooling fan controldriver will close, which should energize fan control relay.
- If A/C fan control switch or circuit is open, the fan would run whenever A/C is requested.
- With A/C clutch engaged, A/C fan control switch should open, when A/C pressure exceeds 200 psi (14 kg/cm 2 ).
- Battery voltage should be available to both terminals "E" and "C" when ignition is on.
- This test checks ability of the ECM to ground circuit No. 335. "SERVICE ENGINE SOON" light should also be flashing at this point. If it isn't flashing, CEC system should be checked.
- If fan does not turn on at this point, circuit No. 702 or circuit No. 150 is open, or cooling fan motor is faulty.
If an overheating condition is suspected, verify if this is due to actual boil over. If gauge or light indicates an overheat condition, and no boil over is in evidence, inspect the gauge/light circuit for malfunction.
If vehicle is overheating and the gauge or light indicates the same, but the cooling fan is not coming on, check coolant sensor temperature using a "SCAN" tester. Sensor may have shifted calibration and should be replaced. If engine is overheating and cooling fan is on, check cooling system.
