Diagnostic Aids
- If the owner complained of an overheating problem, it must be determined if the complaint was due to an actual boil over, or the engine coolant temperature gauge indicated overheating. If the engine is overheating and the cooling fans are on, the cooling system should be checked.
- If the engine fuse block fuses Ef4 or Ef7 become open (blown) immediately after installation, inspect for a short to ground in the wiring of the appropriate circuit. If the fuses become open (blown) when the cooling fans are to be turned on by the Engine Control Module (ECM), suspect a faulty cooling fan motor.
- The ECM will turn the cooling fans on at low speed when the coolant temperature is 205 °F (96 °C).
- The ECM will turn the cooling fans on at high speed when the coolant temperature is 210 °F (99 °C).
- The ECM will turn the cooling fans on at low speed when the A/C system is on. The ECM will change the cooling fans from low speed to high speed when the high side A/C pressure is 270 psi (1,862 kPa) then return to low speed when the high side A/C pressure is 210 psi (1,449 kPa).
- The cooling fan circuit can be checked quickly by disconnecting the ECM white connector and grounding the connector terminal 93. This should create low speed cooling fan operation with the ignition ON. By grounding the ECM connector terminals 93 and 102 and turning the ignition ON, high speed cooling fan operation should be achieved.