I will post the specs here, but first, it seems the pcm is grounding the relay to operate the fan pretty close but not exactly to spec, I would consider a higher range thermostat, install a 195 degree tstat, and see if this helps keeping the heat up.
3.8L "C" & "H" BODIES (BONNEVILLE, EIGHTY EIGHT, LESABRE, LSS, PARK
AVENUE & REGENCY)
Description
Power for fan motors comes from a fusible link at battery junction block. Relays are energized when
current flows from FANS/ACTUATOR fuse through relay coils to ground through PCM. PCM
Output Driver Module (ODM) "B" output No. 1 is grounded for low speed fan operation. PCM ODM
"B" outputs No. 1 and 2 are grounded for high speed operation.
Cooling fan system consists of a single-speed (right side) cooling fan and a dual-speed (left side)
cooling fan. While in low speed (fan No. 1) operation, Light Blue wire supplies a feed directly to
right side cooling fan motor. Left side cooling fan motor is supplied a feed through a resistor, causing
it to run at low speed. When high speed (fan No. 2) operation is commanded, right side fan continues
to run at low speed, but Black wire supplies a feed directly to left side cooling fan motor, causing it
to run at high speed.
Powertrain Control Module (PCM) commands low speed fan operation when vehicle speed is less
than 58 MPH and coolant temperature is greater than 212°F (100°C), or vehicle speed is less than 40
MPH, intake air temperature is greater than 48°F (9°C), and A/C refrigerant pressure is greater than
190 psi (13.4 kg/cm2 ).
High speed fan operation is commanded when vehicle speed is less than 65 MPH and engine coolant
is greater than 226°F (108°C), or vehicle speed is less than 50 MPH and A/C refrigerant pressure is
greater than 260 psi (18.3 kg/cm2 ).
Cooling Fan Circuit Diagnosis
1. If Powertrain On-Board Diagnostic (OBD) System Check has not been performed, see
appropriate TESTS W/CODES article in ENGINE PERFORMANCE section. If OBD
SYSTEM CHECK has been performed, go to next step.
2. Check for PCM Diagnostic Trouble Codes (DTCs). If any DTCs are present, perform testing
for applicable DTC. Some DTCs will cause fans to come on at all times, so repair all DTCs
that are set before proceeding with testing. See appropriate TESTS W/CODES article in
ENGINE PERFORMANCE section. If no DTCs are present, go to next step.
3. Ensure coolant temperature is less than 212°F (100°C). Turn A/C off. Start engine. If cooling
fans are running, go to step 30). If cooling fans are not running, go to next step.
4. Using scan tool, select RELAY CONTROL function. Command low speed fans on. If both
fans run at low speed, go to next step. If both fans do not run at low speed, go to step 8).
5. Command high speed fan on. If left-side cooling fan runs at high speed, go to next step. If left-
side cooling fan does not run at high speed, go to step 18).
6. Ensure ambient temperature is greater than 48°F (9°C). Exit scan tool OUTPUT TESTS. Start
engine and let idle. Turn A/C on. If cooling fans come on, go to DIAGNOSTIC AIDS. If
cooling fans do not come on, go to next step.
7. Using scan tool, view A/C REQUEST on display. If scan tool displays YES, go to step 44). If
scan tool does not display YES, perform A/C clutch diagnosis. See appropriate A/C CLUTCH
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CIRCUIT DIAGNOSIS TEST in A/C COMPRESSOR CLUTCH CONTROLS article.
8. Turn ignition off. Disconnect low speed cooling fan relay. Turn ignition on. Using a test light
connected to ground, probe low speed cooling fan relay harness connector terminal No. 85
(Brown wire). If test light illuminates, go to next step. If test light does not illuminate, go to
step 28).
9. With test light still connected to ground, probe low speed cooling fan relay harness connector
terminal No. 30 (Red wire). If test light illuminates, go to next step. If test light does not
illuminate, go to step 29).
10. Connect fused jumper between low speed cooling fan relay harness connector terminals No. 87
(Light Blue wire) and No. 30 (Red wire). If both cooling fans run at low speed, go to next step.
If both cooling fans do not run at low speed, go to step 14).
11. Using scan tool, select RELAY CONTROL function. Command low speed fans on. Using a
test light connected to battery voltage, probe low speed cooling fan harness connector terminal
No. 86 (Dark Green wire). If test light illuminates, go to step 40). If test light does not
illuminate, go to next step.
12. Turn ignition off. Disconnect PCM harness connector C1. Check circuit No. 335 (Dark Green
wire) for an open or short to voltage between PCM and low speed cooling fan relay. If a
problem is found, repair as necessary, then go to step 46). If no problem is found, go to next
step.
13. Check circuit No. 335 (Dark Green wire) for a poor terminal connection at PCM. If a problem
is found, repair as necessary, then go to step 46). If no problem is found, go to step 44).
14. Disconnect both cooling fan motor harness connectors. Leave low speed cooling fan relay
harness connector terminals No. 87 and 30 jumpered. Using a test light connected to ground,
probe terminal "B" (Black or Light Blue wire) at both fan motor connectors. If test light
illuminates at both fan connectors, go to next step. If test light does not illuminate at both fan
connectors, go to step 16).
15. Connect a test light between terminals "A" and "B" at both cooling fan harness connectors. If
test light illuminates at both harness connectors, go to step 45). If test light does not illuminate
at both harness connectors, go to step 17).
16. Locate and repair open circuit in Black or Light Blue wire. After repairs, go to step 46).
17. Locate and repair open in ground circuit to affected cooling fan motors(s). After repairs, go to
step 46).
18. Disconnect high speed cooling fan relay. Turn ignition on. Using a test light connected to
ground, probe high speed cooling fan relay harness connector terminal No. 30 (Red wire). If
test light illuminates, go to next step. If test light does not illuminate, go to step 29).
19. With test light still connected to ground, probe high speed cooling fan relay harness connector
terminal No. 85. If test light illuminates, go to next step. If test light does not illuminate, go to
step 28).
20. Connect a fused jumper between high speed cooling fan relay harness connector terminals No.
30 (Red wire) and No. 87 (Black wire). If left cooling fan runs at high speed, go to next step. If
left cooling fan does not run at high speed, go to step 24).
21. Using scan tool, select RELAY CONTROL function. Command high speed fan on. Using a
test light connected to battery voltage, probe high speed cooling fan harness connector terminal
No. 86 (Dark Blue wire). If test light illuminates, go to step 42). If test light does not
illuminate, go to next step.
22. Turn ignition off. Disconnect PCM harness connector C1. Check circuit No. 473 (Dark Blue
wire) for an open or short to voltage between PCM and high speed cooling fan relay. If a
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problem is found, repair as necessary, then go to step 46). If no problem is found, go to next
step.
23. Check circuit No. 473 for a poor terminal connection at PCM. If a problem is found, repair as
necessary. After repairs, go to step 46). If no problem is found, go to step 44).
24. Disconnect left-side cooling fan motor connector (leave high speed cooling fan relay harness
connector terminals No. 30 and 87 jumpered). Using a test light connected to ground, probe
left-side cooling fan motor harness connector terminal "B" (Black wire). If test light
illuminates, go to next step. If test light does not illuminate, go to step 27).
25. Connect a test light between left-side cooling fan motor harness connector terminals "A" and
"B" (Black and Light Blue wires). If test light illuminates, go to step 45). If test light does not
illuminate, go to next step.
26. Locate and repair open in ground circuit to left-side cooling fan motor. Repair as necessary,
then go to step 46).
27. Locate and repair open in Black wire to left-side cooling fan motor. After repairs, go to step
46).
28. Locate and repair open in ignition feed circuit (Brown wire) to high speed cooling fan relay.
After repairs, go to step 46).
29. Locate and repair open or short to ground in battery feed circuit (Red wire) to affected cooling
fan relay. After repairs, go to step 46).
30. Disconnect high speed cooling fan relay. If either cooling fan is on, go to step 35). If neither
cooling fan is on. Go to step 31).
31. Using a test light connected to battery voltage, probe high speed cooling fan relay harness
connector terminal No. 86 (Dark Blue wire). If test light is on, go to next step. If test light is
not on, go to step 43).
32. Observe A/C refrigerant pressure reading on scan tool. If A/C refrigerant pressure is greater
than 260 psi (18.2 kg/cm2 ), problem is with A/C system. If pressure is less than 260 psi (18.2
kg/cm2 ), go to next step.
33. Turn ignition off. Disconnect PCM harness connector C1. Turn ignition on. Using a test light
connected to battery voltage, probe high speed cooling fan relay harness connector terminal
No. 86 (Dark Blue wire). If test light illuminates, go to next step. If test light does not
illuminate, go to step 44).
34. Locate and repair short to ground in circuit No. 473 (Dark Blue wire). After repairs, go to step
46).
35. Disconnect low speed cooling fan relay. If either cooling fan is on, go to step 39). If neither
cooling fan is on, go to step 36).
36. Using a test light connected to battery voltage, probe low speed cooling fan relay harness
connector terminal No. 86 (Dark Green wire). If test light illuminates, go to next step. If test
light does not illuminate, go to step 41).
37. Turn ignition off. Disconnect PCM harness connector C1. Turn ignition on. With test light still
connected to battery voltage, probe low speed cooling fan relay harness connector terminal No.
86 (Dark Green wire). If test light illuminates, go to next step. If test light does not illuminate,
go to step 44).
38. Locate and repair short to ground in circuit No. 335 (Dark Green wire). After repairs, go to
step 46).
39. Locate and repair short to power in affected cooling fan motor power feed circuit. After
repairs, go to step 46).
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40. Check for poor connection at low speed cooling fan relay. If problem is found, repair as
necessary, then go to step 46). If no problem is found, go to next step.
41. Replace low speed cooling fan relay. After replacing relay, go to step 46).
42. Check for poor connection at high speed cooling fan relay. If a problem is found, repair as
necessary, then go to step 46). If no problem is found, go to next step.
43. Replace high speed cooling fan relay. After replacing relay, go to step 46).
44. Replace PCM. After replacing PCM, go to step 46).
45. Replace affected cooling fan motor. After replacing motor, go to next step.
46. Ensure engine coolant temperature is less than 212°F (100°C). Turn A/C off. Start engine and
let idle. If cooling fans operate, go to step 30). If cooling fans do not operate, go to next step.
47. Using scan tool, select RELAY CONTROL function. Command low speed fans on. If both
fans run at low speed, go to next step. If both fans do not run at low speed, go to step 8).
48. Command high speed cooling fan on. If left-side cooling fan runs at high speed, system is
operating normally at this time. If left-side cooling fan does not run at high speed, go to step
18).
Diagnostic Aids
Check for poor connections at PCM, cooling fan relays and cooling fan motors. Inspect harness
connectors for damaged, corroded or backed-out terminal pins. Inspect related wiring harnesses for
damage or improper routing.
Wednesday, December 29th, 2010 AT 7:48 PM
