HI,

PCM(ECM) problem/question please:

My 1996 Buick Century 3.1L w/130K miles VIN 1G4AG55MXT6414148 was perfect/everything working, no DTC'*,
Except cruise control not working AND a problem of the AC condenser pusher-fan relay not ever coming on because I found the ground signal from the PCM is too weak to close the relay, even though the wiring tests fine from the relay to the PCM and other relays were tried/swapped.

THEN while diagnosing, I plugged in my Xtool A30M scanner $160 that has some bi-directional functionality.
I told it to tell the PCM to turn on the radiator pull fan(which was fine). But it did not turn the fan on.
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And Now, the radiator pull fan will not come on as well, AND, the car will not shift into first gear even manually and will not down shift Any during under full throttle and there are now several DTC'* concerning the radiator fan & AC fan(P1651, P1652), and the transmission(P0753, P0756, P0758, P1864).
The transmission codes will not clear and the other codes come back immediately upon driving.
I've even disconnected the battery posts and held the pos neg wires together to try to clear/reset to the way it was.
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So.... it seems to me that the OBD2 scanner damaged the PCM and now I need to replace it to fix all the problems.

My PCM: Serv. NO. 16211539. BSXB

*86BSXBK35276EZ76*.

I see some sellers on E-bay for $65 who will program to my vin and mail a remanufactured/tested PCM of the same 16211539 number and it says it'* compatible.
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The car is parked for now till I fix this all.

Would you say that is what I should do, replace the PCM, or is there something else to try or are the transmission problems unrelated to my scanner use?

Thank-you for any help.

Jim McDaniels

Have you done any testing? Are the grounds in good order? I have the factory info if you need something let me know.
I seriously do not think the scan tool did any damage. You may have done something messing around the fuse/relay center.

Thank you for the reply Carfixer007,

I also have the 2 original shop manuals.
Yes I had disconnected the car battery and then the 2 cable groups, clear and blue, to the PCM and tested the connections that supply ground to the PCM, all tested good and the one that supplies ground back to the pusher fan relay for any resistance.
I was careful not to touch any of the PCM pins.

Another site thinks my evidently cheap Chinese clone scanner did damage the PCM and it seems too much evidenced since the radiator fan DTC is on after I used the bi directional command to tell it to come on.

Seems I need a replacement PCM anyway to hopefully fix the original problem that traced back to the PCM, the AC pusher fan not turning on.

So first I'm going to order the $70 PCM on eBay(with return policy) and see how it goes.

I'll report back here so others can learn from my mis-takes and how this plays out next.

Thank-you

Jim

UPDATE(can drive the car again):

Ok the Ebay reprogrammed PCM is doing the same thing. So I went back to the dealer service manuals and focused on the radiator fan which use to work.
I found that there was no longer a positive feed to its relay electromagnet pin with the ignition on. So I saw in the manual there is a hidden 10 amp inline fuse that can blow.
The manual said it was on the driver'* side, but the internet said the passenger side behind-to the right of the fuse panel with the glove box removed.
There I found it and 2 other spade fuses black electric taped together(10 amp, 15 amp, 20 amp).
Sure enough the 10 amp fuse was blown and once I replaced it everything was back to the way it was and trouble codes cleared and the transmission working great again and not starting out in 2nd...

I'm going to try to find out the purpose of the other 2 fuses and label them and my fuse box so we know there are hidden fuses wow surprised gm did that..

SO it seems I just have blown that 10 amp fuse doing a few things between using my scanner. I assume the scanner probably didn't/couldn't blow that fuse..or maybe the bi-direction function did. Grr

But I'm back to the same problems of the pusher fan not coming on ever even with the compressor running and engine warmed up.
Even though the I've swapped it with the radiator fan relay and it works there running the radiator fan.
Even though the positive electromagnet feed is good, the positive power is good. I can jump the pos to fan motor pos and the fan runs.
The negative from the PCM is weak for some reason..seems the problem and the wiring tested good.

Also the cruise control not working even though I've gone through the manual tests. It'd be nice to get those working again.
I think I need to do a new post for those problems.

Thank you

PS: I found the purpose of the 3 fuses are from memory lol:

10 Amp Cooling Fans, Trans, EVAP, etc

15 Amp Air Bag Module, Security system(makes sense to hide that fuse)

20 Amp Trans speed range, Data Link, etc



In case anyone finds this info helpful in the future.

Its possible the AC components are meant to trigger the fans for the car and not the PCM.

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3.1L - VIN M ("A" & "W" BODIES)

DESCRIPTION

Cooling fan relay coils are energized when PCM completes ground path. PCM Output Driver Module (ODM) "B" output No. 1 is grounded for fan No. 1 operation. PCM ODM "B" output No. 2 is grounded for fan No. 2 operation.

During fan No. 1 operation PCM supplies a ground path for fan No. 1 relay through ODM "B" output No. 1. This closes fan No. 1 relay contacts and current flows through relay and to primary cooling fan. Primary cooling fan is grounded at engine block.

During fan No. 2 operation, PCM keeps fan No. 1 energized and supplies a ground path for fan No. 2 relay. This closes fan No. 2 relay contacts and current flows through fan No. 2 to engine ground.

COOLING FAN CIRCUIT DIAGNOSIS

NOTE: Ambient temperature must be greater than 48°F (9°C) before PCM will enable cooling fans due to A/C request. PCM will enable cooling fans if A/C refrigerant pressure increases regardless of ambient temperature.

1. If Powertrain On-Board Diagnostic (OBD) System Check has not been performed, see appropriate TESTS W/CODES article. If OBD system check has been performed, go to next step.
2. Check for PCM Diagnostic Trouble Codes (DTCs). If any codes are present, perform testing for applicable code. Repair all DTCs that are set before proceeding with testing. See appropriate TESTS W/CODES article. If no codes are present, go to next step.
3. Ensure engine coolant temperature is less than 212°F (100°C). Turn A/C off. Turn ignition on. If cooling fans go off, go to next step. If cooling fans do not go off, go to step 43).
4. Select scan tool MISC. TESTS, RELAY CONTROL function, and command fan No. 1 on. If fan comes on, go to next step. If fan does not come on, go to step 6).
5. Select scan tool MISC. TESTS, RELAY CONTROL function and command fan No. 2 on. If fan No. 2 does not come on, go to step 19). If fan No. 2 does come on, system is operating normally.
6. Remove fan No. 1 relay from right underhood electrical center. Turn ignition on, engine off. Connect test light between fan relay connector terminals No. 85 (Pink wire) and No. 86 (Dark Green wire). Select scan tool MISC. TESTS, RELAY CONTROL function and command fan No. 1 on. If test light illuminates, go to next step. If test light does not illuminate, go to step 15).
   
7. Check for blown Blue Maxi-fuse No. 3 (60-amp). If fuse is blown, go to step 19). If fuse is not blown, go to next step.
8. Connect test light between ground and fan No. 1 relay connector terminal No. 30 (Red wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 10).
9. Locate and repair open battery feed circuit to terminal No. 30 (Red wire) in fan No. 1 relay connector. After repairs, go to step 56).
10. Turn ignition off. Connect a 20-amp fused jumper wire between terminals No. 30 (Red wire) and No. 87 (Light Blue wire) in fan No. 1 relay connector. If fan No. 1 is running, go to next step. If fan No. 1 is not running, go to step 53).
11. Disconnect fan No. 1 electrical connector. Install 20-amp fused jumper wire between fan No. 1 relay connector terminals No. 30 (Red wire) and No. 87 (Light Blue wire). Connect test light between fan No. 1 harness connector terminals. If test light illuminates, go to step 52). If test light does not illuminate, go to next step.
12. Connect test light between battery voltage and cooling fan motor No. 1 ground circuit at fan No. 1 connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 14).
13. Locate and repair open circuit in engine cooling fan motor No. 1 voltage circuit. After repairs, go to step 56).
14. Locate and repair open circuit in engine cooling fan motor No. 1 ground circuit. After repairs, go to step 56).
15. Connect test light between ground and fan No. 1 relay connector terminal No. 85 (Pink wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 17).
16. Turn ignition off. Disconnect PCM harness connector. Connect test light between terminals No. 85 (Pink wire) and No. 86 (Dark Green wire) at fan No. 1 relay connector. Connect jumper wire between fan No. 1 relay driver circuit and ground at PCM connector. If test light illuminates, go to step 51). If test light does not illuminate, go to step 1.
17. Locate and repair open circuit in battery feed circuit to terminal No. 85 (Pink wire) in fan No. 1 relay connector. After repairs, go to step 56).
18. Locate and repair open circuit in fan No. 1 relay driver circuit. After repairs, go to step 56).
19. Remove Blue Maxi-fuse fuse No. 3 (60-amp). Connect a test light between voltage and fan No. 1 relay connector terminal No. 30 (Red wire) at fan No. 1 relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 21).
20. Locate and repair short to ground in battery feed circuit to terminal No. 30 (Red wire) in fan No. 1 relay connector. After repairs, go tostep 56).
21. Disconnect engine cooling fan motor No. 1 connector. Connect test light between battery voltage and terminal No. 87 (Light Blue wire) at fan No. 1 relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 52).
22. Locate and repair short to ground in engine cooling fan motor No. 1 feed circuit. After repairs, go to step 56).
23. Remove fan No. 2 relay from right underhood electrical connector. Turn ignition on, engine off. Connect test light between terminals No. 85 and 86 in relay connector. Select scan tool MISC. TEST, RELAY CONTROL function and command fan No. 2 on. If test light illuminates, go to next step. If test light does not illuminate, go to step 32).
24. Check for a blown Blue Maxi-fuse No. 3 (60-amp) that feeds fan No. 2 relay terminal No. 30. If fuse is blown, go to step 39). If fuse is not blown, go to next step.
25. Connect a test light to ground. Probe terminal No. 30 in fan No. 2 relay connector. If test light illuminates, go to step 27). If test light does not illuminate, go next step.
26. Locate and repair open in feed circuit to fan No. 2 relay, terminal No. 30. After repairs, go to step 56).
27. Turn ignition off. Connect a 20-amp fused jumper between terminals No. 30 and 87 at fan No. 2 relay connector. Turn ignition on. If fan No. 2 is on, go to step 54). If fan No. 2 is not on, go to next step.
28. Disconnect engine cooling fan motor No. 2 electrical connector. Connect a 20-amp fused jumper wire between terminals No. 30 and 87 at fan No. 2 relay connector. Connect a test light between the engine cooling fan motor No. 2 connector terminals. If test light illuminates, go to step 54). If test light does not illuminate, go to next step.
29. Using test light connected to battery voltage, probe ground circuit terminal at engine cooling fan motor No. 2 connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 31).
30. Locate and repair open in engine cooling fan motor No. 2 feed circuit. After repairs, go to step 56).
31. Locate and repair open in engine cooling fan motor No. 2 ground circuit. After repairs, go to step 56).
32. Check fuse that feeds fan No. 2 relay terminal No. 85. If fuse is blown, go to next step. If fuse is not blown, go to step No. 35).
33. Remove in-line fuse (10-amp) that feeds fan No. 2 relay terminal No. 85. Probe terminal No. 85 at fan No. 2 relay connector with a test light to voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 55).
34. Locate and repair short to ground in feed circuit to fan No. 2 relay terminal No. 85. After repairs, go to step 56).
35. Probe terminal No. 85 in fan No. 2 relay connector with a test light to ground. If test light illuminates, go next step. If test light does not illuminate, go to step 37).
36. Turn ignition off. Disconnect PCM connector. Connect a test light between terminals No. 85 and 86. at fan No. 2 relay connector. Jumper fan No. 2 relay driver circuit to ground at PCM connector. If test light illuminates, go to step 51). If test light does not illuminate, go tostep 3.
37. Locate and repair open circuit in feed circuit to fan No. 2 relay connector terminal No. 85. After repairs, go to step 56).
38. Locate and repair open circuit in fan No. 2 driver circuit. After repairs, go to step 56).
39. Remove Blue Maxi-fuse No. 1 (60-amp). Connect a test light to battery voltage. Probe terminal No. 30 at fan No. 2 relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 41).
40. Locate and repair short to ground in feed circuit to fan No. 2 relay connector terminal No. 30. After repairs, go to step 56).
41. Disconnect engine cooling fan motor No. 2 connector. Probe terminal No. 87 in fan No. 2 relay connector with a test light to voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 54).
42. Locate and repair short to ground in engine cooling fan motor No. 2 feed circuit. After repairs, go to step 56).
43. If both cooling fans are on, go to next step. If both fans are not on, go to step 45).
44. Turn ignition off. Disconnect A/C pressure sensor. Turn ignition on. Using scan tool, monitor A/C pressure. If scan tool shows zero psi, go to step 49). If scan tool does not show zero psi, go to step 51).
45. If cooling fan No. 1 is on, go to next step. If cooling fan No. 1 is not on, go to step 50).
46. Use scan tool and monitor A/C pressure. If scan tool shows pressure greater than 190 psi (13.4 kg/cm2 ), go to step 47). If scan tool does not show pressure greater than 190 psi (13.4 kg/cm2 ), go tostep 4.
47. Disconnect A/C pressure sensor. Using scan tool, monitor A/C pressure. If scan tool shows zero psi, go to step 49). If scan tool does not show zero psi, go to step 51).
48. Locate and repair short in cooling fan motor No. 1 feed circuit. After repairs, go to step 56).
49. Replace A/C pressure sensor. After replacing pressure sensor, go to step 56).
50. Locate and repair short in engine cooling fan motor No. 2 feed circuit. After repairs, go to step 56).
51. Replace PCM. After replacing PCM, go to step 56).
52. Replace engine cooling fan motor No. 1. After replacing motor, go to step 56).
53. Replace fan No. 1 relay. After replacing relay, go to step 56).
54. Replace engine cooling fan motor No. 2. After replacing motor, go to step 56).
55. Replace fan No. 2 relay. After replacing relay, go to next step.
56. Ensure engine coolant is less than 212°F (100°C). Turn A/C switch off. Turn ignition on. If fans are off, go to next step. If fans are not off, go to step 3).
57. Select scan tool MISC. TESTS, RELAY CONTROL function and command fan No. 1 on. If fan comes on, go to next step. If fan does not come on, go to step 6).
58. Select scan tool MISC. TESTS, RELAY CONTROL function and command fan No. 2 on. If fan comes on, system is operating normally at this time. If fan does not come on, go to step 19).

Thank you,

I do have the 2 OEM service manuals that have much detail.
What you provided is a nice step by step walk through trouble shooting.

I read through it and it doesn't change my concluding that the PCM circuit driver for the pusher fan is bad.

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Someone on Buickforums.com said they had the same problem on their 2001 and a replacement PCM fixed the problem.

Well I've went ahead and did the PCM bypass with the help of a salvage yard plug with relay and some wire crimp connectors and labeled it all and in my repair records.



I've attached a pic. The PCM now only connects to the dummy salvage yard relay and plug to keep from the check engine light coming on.



The pusher fan original relay electro magnet is now permanently grounded to a grounding bolt instead of the PCM. Then the magnet'* positive is triggered and powered by the radiator fan'* motor juice coming on.



The Ebay rebuilt PCM I'm going to return. I got it when I thought my scanner blew to the PCM but instead I had a blown 10 amp fuse hidden behind the glove box wrapped in oem electric tape with 2 other in line fuses. I will have to pay shipping. I think I'll slip them a $10 for their time and trouble.



Thank you for the response.



Jim

Where did/do you get those updates list online?

I suppose it means someone reprogramming the PCM can add those enhancements if they use the latest software?
Complicated interesting stuff.

Thank you

did your car come with a shorting bar in the DLC connector?