Component Tests and General Diagnostics

If coolant fan does not run at all, perform test A. If coolant fan does not turn off with engine coolant cool, A/C Off and ignition switch in RUN position, perform test B. If coolant fan does not turn On with A/C On and head pressure above 223 psi, but does turn On with engine hot, perform test C.


Test A: Coolant Fan Open Test

1. Connect fused jumper between ALDL connector terminal B and ground and turn ignition switch to RUN position. If coolant fan runs, problem is ECM related.
2. If coolant fan does not run, connect fused jumper to coolant fan relay connector between dark green/white wire and ground and turn ignition switch to RUN position. If coolant fan runs, check dark green/white wire for open. If wire is satisfactory, problem is ECM related.
3. If coolant fan does not run, disconnect coolant fan relay connector, turn ignition switch to run position and connect test lamp between terminals as follows:
a. Connect between terminal D and ground. If lamp does not illuminate, check C/H-FAN fuse, tan/white wire for open.
b. Connect between red wire terminal and ground. If lamp does not illuminate, check fusible link J and red wire for open.
4. If lamp illuminates in steps a and b, disconnect coolant fan relay connector and connect fused jumper between red and black/red wire terminals. If coolant fan runs, replace coolant fan relay.
5. If coolant fan does not run, leave fused jumper connected as in step 4, disconnect coolant fan connector and connect test lamp between terminals as follows:
a. Connect between black/red wire terminal and ground. If lamp does not illuminate, check black/red wire for open.
b. Connect between black/red and black wire terminals. If lamp does not illuminate, check black wire for open.
c. If lamp illuminates in steps a and b, replace coolant fan.

Test B: Coolant Fan Does Not Turn Off With Engine Coolant Cool, A/C Off And Ignition Switch In RUN Position

1. Disconnect coolant fan relay, connect a test lamp between terminals D and F of the fan relay connector. If lamp does not light, replace coolant fan relay.
2. If test lamp lights, check and repair dark green/white wire for a short to ground. If wire is satisfactory, connect a fused jumper between terminal C2/D12 of the ECM and ground.
3. After waiting two minutes if fan continues to run, problem is ECM related.
4. If fan stops, disconnect fan A/C pressure switch connector and connect a fused jumper between terminal B and ground.
5. After two minutes if fan continues to run, check dark blue wire for an open.
6. If fan stops, connect a fused jumper between terminals B and A of the fan A/C pressure switch connector. If fan continues to run, Repair open in black/white wire.
7. If fan stops, replace fan A/C pressure switch.

TEST C: Coolant Fan Does Not Turn On With A/C On And Head Pressure Above 223 psi, But Does Turn On With Engine Hot

1. With ignition switch in RUN position and A/C mode selector in MAX position, disconnect fan A/C pressure switch connector. Measure voltage between terminal B and ground. If zero volts is present, repair short to ground in dark green/white wire.
2. If battery voltage is present, problem is ECM related.