System Diagnosis

Coolant Fan Does Not Run

1. Connect fused jumper between ALDL connector 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 between ECM connector C1 (VIN K) or C3 (VIN M) dark green/white wire and ground and turn ignition switch to RUN position. If coolant fan runs, problem is ECM related.
3. If coolant fan does not run, leave fused jumper connected as in step 2, disconnect coolant fan relay connector, turn ignition switch to RUN position and connect test lamp between terminals as follows:
a. Connect between terminal 1 and ground. If lamp does not illuminate, check red wire and fusible link C for open.
b. Connect between terminal 5 and ground. If lamp does not illuminate, check brown wire (VIN K) or red (2) wire (VIN M) for open.
c. Connect between terminals 5 and 2. If lamp does not illuminate, check dark green/white wire for open.
4. If lamp illuminates in steps a, b and c, disconnect coolant fan relay connector and connect fused jumper between terminals 1 and 4. If coolant fan runs, replace coolant fan relay.
5. If coolant fan does not run, connect fused jumper between terminals 1 and 4 of coolant fan relay, disconnect coolant fan connector and connect test lamp between terminals as follows:
a. Connect between terminal B and ground. If lamp does not illuminate, check black/red wire for open.
b. Connect between terminals B and A. If lamp does not illuminate, check black wire for open.
c. If test lamp illuminates in steps a and b, replace coolant fan.

Coolant Fan Runs Continuously

1. Place ignition switch in RUN position, disconnect coolant fan relay connector and connect test lamp between terminals 5 and 2.
2. If test lamp does not illuminate, replace coolant fan relay.
3. If lamp illuminates, check dark green/white wire for short to ground. If wire is satisfactory, problem is ECM related.