MERGED-(Fresh opti pull pics) & (Ignition stutter-Code crackers needed)
Thread Starter
Instructor
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From: OH/FL
Just read your post, and my thoughts while in the showah..
1) If *29* is the problem, when fan engages at around 215degress could the load it places on the PCM be causing it to malfunction?
2) if *29* is on same circuit (somehow) as Opti, can fan load be degrading the ICC signal, causing H41 and H42?
Those are the only two theories I can come up with tonight. 12:22am...tired, but squeaky clean...going to bed...
Again...I think hours of pining over harnesses could be averted if a good PCM solves these problems. Worst case scenario there is new PCM into '95 Vette with unresolved electrical issue could lead to another bunk PCM...
Ok...NOW I'm going to bed...7:30am meeting.
1) If *29* is the problem, when fan engages at around 215degress could the load it places on the PCM be causing it to malfunction?
2) if *29* is on same circuit (somehow) as Opti, can fan load be degrading the ICC signal, causing H41 and H42?
Those are the only two theories I can come up with tonight. 12:22am...tired, but squeaky clean...going to bed...
Again...I think hours of pining over harnesses could be averted if a good PCM solves these problems. Worst case scenario there is new PCM into '95 Vette with unresolved electrical issue could lead to another bunk PCM...
Ok...NOW I'm going to bed...7:30am meeting.
Safety Car
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Okay - I got somethin' else to do diagnostic (see the smoke from my noggin'?)
Look at the schematic here: see how the circuit splits off from fuse 29? We're going to disconnect the primary fan relay, AND disconnect the primary fan relay-to-PCM connection.
THEN, we're gonna' route the secondary fan relay into the PCM input FROM the primary fan relay.
We're gonna' make the PCM think it's runnin the primary fan stuff, but it's really runnin' the secondary fan stuff.
Gimme' five to post the FSM schematic...
Look at the schematic here: see how the circuit splits off from fuse 29? We're going to disconnect the primary fan relay, AND disconnect the primary fan relay-to-PCM connection.
THEN, we're gonna' route the secondary fan relay into the PCM input FROM the primary fan relay.
We're gonna' make the PCM think it's runnin the primary fan stuff, but it's really runnin' the secondary fan stuff.
Gimme' five to post the FSM schematic...
Safety Car
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I Got It I GOT IT I GOT IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Icc Fault Trips When Cooling Fan Comes On. That We Know.
So, Here's What We Do:
Icc Fault Trips When Cooling Fan Comes On. That We Know.
So, Here's What We Do:
Last edited by schrade; Jul 18, 2008 at 01:14 AM.
Thread Starter
Instructor
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From: OH/FL
I'm going to work right now, but I'm telling you...despite your investigation, if I have to jump a wire, THE PCM IS BAD. If I have to "fool" a circuit, THE PCM IS BAD. 
Again, I'll try your solutions tonight after work, my friend...
Again, I'll try your solutions tonight after work, my friend...
Thread Starter
Instructor
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From: OH/FL
Hey...at work now (sshhhh!!!)
Against your better judgement, I pulled the fuse this morning. Drove the car up to operating temp, drove on the highway, surface roads, little over 8 miles and the temp never got above 225.......the engine popped a little, but no codes and generally ran very smoothly.
Went to a two hour meeting...came out and started the car. Temp was 180 degrees and instantly the CEL light came on and it burbled like usual. It performed the exact same way for the next 15 miles on the highway...then downtown surface streets. Temp got to about 238 until I shut it down at my offices.
Pulled codes with my trusty bent paperclip in the parking lot (wearing a suit, nonetheless!)...H41....H42....H77....H78 ...
Thoughts:
1) Even though the load from the fan was never placed on the electrical system, the act of starting up the warm engine messed with the faulty circuit...whether in a wiring harness or PCM?
2) The PCM is just toast, and goes into a "limp mode" when it gets warm and anything from A/C to the cooling fan puts an electrical load on the system...
3) While the cooling fan was disabled, the A/C system sent the PCM into H41-H42-land instantaneously when it engaged as I started the car.
Against your better judgement, I pulled the fuse this morning. Drove the car up to operating temp, drove on the highway, surface roads, little over 8 miles and the temp never got above 225.......the engine popped a little, but no codes and generally ran very smoothly.
Went to a two hour meeting...came out and started the car. Temp was 180 degrees and instantly the CEL light came on and it burbled like usual.
It performed the exact same way for the next 15 miles on the highway...then downtown surface streets. Temp got to about 238 until I shut it down at my offices.Pulled codes with my trusty bent paperclip in the parking lot (wearing a suit, nonetheless!)...H41....H42....H77....H78 ...
Thoughts:
1) Even though the load from the fan was never placed on the electrical system, the act of starting up the warm engine messed with the faulty circuit...whether in a wiring harness or PCM?
2) The PCM is just toast, and goes into a "limp mode" when it gets warm and anything from A/C to the cooling fan puts an electrical load on the system...
3) While the cooling fan was disabled, the A/C system sent the PCM into H41-H42-land instantaneously when it engaged as I started the car.
Safety Car
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From: :45 minutes from everywhere / E-I-E-I-O
Hey...at work now (sshhhh!!!)
Against your better judgement, I pulled the fuse this morning. Drove the car up to operating temp, drove on the highway, surface roads, little over 8 miles and the temp never got above 225.......the engine popped a little, but no codes and generally ran very smoothly.
Went to a two hour meeting...came out and started the car. Temp was 180 degrees and instantly the CEL light came on and it burbled like usual. It performed the exact same way for the next 15 miles on the highway...then downtown surface streets. Temp got to about 238 until I shut it down at my offices.
Pulled codes with my trusty bent paperclip in the parking lot (wearing a suit, nonetheless!)...H41....H42....H77....H78 ...
Thoughts:
1) Even though the load from the fan was never placed on the electrical system, the act of starting up the warm engine messed with the faulty circuit...whether in a wiring harness or PCM?
2) The PCM is just toast, and goes into a "limp mode" when it gets warm and anything from A/C to the cooling fan puts an electrical load on the system...
3) While the cooling fan was disabled, the A/C system sent the PCM into H41-H42-land instantaneously when it engaged as I started the car.
Against your better judgement, I pulled the fuse this morning. Drove the car up to operating temp, drove on the highway, surface roads, little over 8 miles and the temp never got above 225.......the engine popped a little, but no codes and generally ran very smoothly.
Went to a two hour meeting...came out and started the car. Temp was 180 degrees and instantly the CEL light came on and it burbled like usual.
It performed the exact same way for the next 15 miles on the highway...then downtown surface streets. Temp got to about 238 until I shut it down at my offices.Pulled codes with my trusty bent paperclip in the parking lot (wearing a suit, nonetheless!)...H41....H42....H77....H78 ...
Thoughts:
1) Even though the load from the fan was never placed on the electrical system, the act of starting up the warm engine messed with the faulty circuit...whether in a wiring harness or PCM?
2) The PCM is just toast, and goes into a "limp mode" when it gets warm and anything from A/C to the cooling fan puts an electrical load on the system...
3) While the cooling fan was disabled, the A/C system sent the PCM into H41-H42-land instantaneously when it engaged as I started the car.
So since (I'm hopin') you didn't clear last night,
1) The fault was already in it this morning.
2) Yes, the PCM COULD be toast, but we're gonna' finish testing each component of each of the 2 fan relay circuit.
3) Again, it was already in there, I think...
At any rate, we'll know by the end of the day - fan component, or PCM...
Safety Car
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...which DOES lean towards a PCM. BUT, to know for sure, let's get the fan parts tested. Won't take an hour...
DO NOT order a PCM yet - if mine and yours are BOTH bad, we might get a deal pickin' up two.
Thread Starter
Instructor
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From: OH/FL
I'll wait for your instructions this evening. TANKS FO' YO' HELP!
P.S...I was a code-clearing mo'fo, so I don't want to hear all this "you didn't do it right" nonsense.
Unless you HAVE to clear 1.7 with clearing 4.7...then I did do it wrong. When 1 has a "C12", I don't bother clearing it. I just clear module 4 when the H41, H42, H77, H78 codes come up, and I make sure I get the "- - -" message before turning the key off...
P.S...I was a code-clearing mo'fo, so I don't want to hear all this "you didn't do it right" nonsense.
Unless you HAVE to clear 1.7 with clearing 4.7...then I did do it wrong. When 1 has a "C12", I don't bother clearing it. I just clear module 4 when the H41, H42, H77, H78 codes come up, and I make sure I get the "- - -" message before turning the key off...
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Safety Car
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From: :45 minutes from everywhere / E-I-E-I-O
I'll wait for your instructions this evening. TANKS FO' YO' HELP!
P.S...I was a code-clearing mo'fo, so I don't want to hear all this "you didn't do it right" nonsense.
Unless you HAVE to clear 1.7 with clearing 4.7...then I did do it wrong. When 1 has a "C12", I don't bother clearing it. I just clear module 4 when the H41, H42, H77, H78 codes come up, and I make sure I get the "- - -" message before turning the key off...
P.S...I was a code-clearing mo'fo, so I don't want to hear all this "you didn't do it right" nonsense.
Unless you HAVE to clear 1.7 with clearing 4.7...then I did do it wrong. When 1 has a "C12", I don't bother clearing it. I just clear module 4 when the H41, H42, H77, H78 codes come up, and I make sure I get the "- - -" message before turning the key off...
And yes, you probably did do it right.
The ICC fault can trip right away, even on a cold motor (another point for bad PCM). It happened to me after the 3-day wires/spark plug swap, with the battery out 3 days.
Right now, I'm waitin' for the Chevy service manager to call me back, to see if there's a common failure in the primary or secondary fan circuit (I doubt it, but let's make sure before buyin' the new PCM). He's the one that loaned me the FSM, so he'll shoot straight.
He just called; he's not understanding as I explain.
I'm gonna' dig in and swap the 2 fan circuits, and see what happens.
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This is where the codes didn't go away... I knew I had posted it somewhere (#24, this thread)...
I got the H41 and H42 immediately when I finished re-assembly. Ain't that a little strange? 
The battery was disconnected for 3 days.
So I just disconnected the battery again, put in my ig module, fired it, and no light - remember, the DTC 41 will NOT light up SES. The fresh DTC H42 did.
I took a spin, warmed it up, came back and checked for codes again (AFTER I pulled the radiator cap to let off pressure - I had forgotten to clamp one WP hose, and it was drainin' some coolant - idiot).
So this time, no codes. I know it didn't fix itself, cause all I did was clean stuff up, and found nothing wrong. Even with my good ig module back in.
Any ideas???
The battery was disconnected for 3 days.So I just disconnected the battery again, put in my ig module, fired it, and no light - remember, the DTC 41 will NOT light up SES. The fresh DTC H42 did.
I took a spin, warmed it up, came back and checked for codes again (AFTER I pulled the radiator cap to let off pressure - I had forgotten to clamp one WP hose, and it was drainin' some coolant - idiot).
So this time, no codes. I know it didn't fix itself, cause all I did was clean stuff up, and found nothing wrong. Even with my good ig module back in.
Any ideas???
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From: :45 minutes from everywhere / E-I-E-I-O
Pick up a bag of ice on your way home. It's hard enough to make sure the H41 is really out of the computer, keepin' it cool will help - I've seen that in threads somewhere (and for home pc hard disk drives too).
Here's our next target - fan relays.
I'm runnin' with them disconnected now. This should not trip the code - it's the same as havin' the fuse pulled - see the schematic a few posts back for fuse 29 and the 2 pinks, 1 dark green, and 1 dark blue wires. According to the schematic, there's nothing between them.
Here's our next target - fan relays.
I'm runnin' with them disconnected now. This should not trip the code - it's the same as havin' the fuse pulled - see the schematic a few posts back for fuse 29 and the 2 pinks, 1 dark green, and 1 dark blue wires. According to the schematic, there's nothing between them.
Last edited by schrade; Jul 18, 2008 at 01:32 PM.
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Fan relays dis-connected...
231 on the temp guage and shutdown; codes H72 (VSS loss, means nada - the vehicle didn't move (bad PCM?)), H77, H78 (1st + 2nd fan circuits fail (OK)).
No H41. It shouldn't have, UNLESS there was a short or open between 29 fuse, and the relays. GOT to check them ALL.
Next, plug in one of the relay connectors. Which one?
Which fan comes on at 228? Primary? Secondary? I don't know where it is in the FSM... I need to know, to plug in the OTHER fan.
231 on the temp guage and shutdown; codes H72 (VSS loss, means nada - the vehicle didn't move (bad PCM?)), H77, H78 (1st + 2nd fan circuits fail (OK)).
No H41. It shouldn't have, UNLESS there was a short or open between 29 fuse, and the relays. GOT to check them ALL.
Next, plug in one of the relay connectors. Which one?
Which fan comes on at 228? Primary? Secondary? I don't know where it is in the FSM... I need to know, to plug in the OTHER fan.
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EVERY TIME YOU SWITCH SOMETHING, DIS-CONNECT THE BATTERY. We're tryin' to keep the computer 'totally in the dark'. AND, the coolant temp has to be below the temp that trips up BOTH fan circuits. Otherwise, as soon as you turn the key to 'ON', the computer gets the signal for high temp, and tries to start the fan. THIS IS WHAT HAPPENED LAST NIGHT WHEN YOU PUT THE FUSE IN HOT AND RUNNING. I should have told you to not do this.
======================================== ==========
See the diagnostic here now...
You said yours starts problems at 215 - 220. How sure are you??? The diagnostic says the PRIMARY fan comes on at 219. Is your ICC tripped up by the PRIMARY FAN??? We need to know that. All we know now is that 1 or the other does, and maybe both.
If it trips at 219, then YOU plug in the secondary relay, and test.
If it is above 220, like about 228, then YOU try with the PRIMARY plugged in.
We need also to know if '95 fan temperature specs are the same...
Mine is tripping ICC fault when the secondary fan starts. I am about to try with the primary plugged in...
======================================== ==========
See the diagnostic here now...
You said yours starts problems at 215 - 220. How sure are you??? The diagnostic says the PRIMARY fan comes on at 219. Is your ICC tripped up by the PRIMARY FAN??? We need to know that. All we know now is that 1 or the other does, and maybe both.
If it trips at 219, then YOU plug in the secondary relay, and test.
If it is above 220, like about 228, then YOU try with the PRIMARY plugged in.
We need also to know if '95 fan temperature specs are the same...
Mine is tripping ICC fault when the secondary fan starts. I am about to try with the primary plugged in...
Last edited by schrade; Jul 19, 2008 at 02:15 AM.
Safety Car
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First fan test, to set ICC fault code:
Primary relay plugged in, secondary dis-connected. Ran the temp to 221; shutdown.
(Secondary fan code will not set - we did NOT reach 228) Right? RIGHT! The computer did as it was supposed to do/did not do what it was not supposed to do. Score one for the computer.
Primary fan DID NOT come on at 219 as per spec. ???
Primary fan code is set - right? Wrong - did NOT set Primary fan fault. HUH???
So the computer thinks the fan did it's gig. BUT, we had no amp draw to possibly set the ICC fault code. We have to make the primary fan come on to see if it sets the ICC fault.
First, see if the fan will jump - motor off.
Whew! What time is it? What year is it?
Primary relay plugged in, secondary dis-connected. Ran the temp to 221; shutdown.
(Secondary fan code will not set - we did NOT reach 228) Right? RIGHT! The computer did as it was supposed to do/did not do what it was not supposed to do. Score one for the computer.
Primary fan DID NOT come on at 219 as per spec. ???
Primary fan code is set - right? Wrong - did NOT set Primary fan fault. HUH???
So the computer thinks the fan did it's gig. BUT, we had no amp draw to possibly set the ICC fault code. We have to make the primary fan come on to see if it sets the ICC fault.
First, see if the fan will jump - motor off.
Whew! What time is it? What year is it?
Safety Car
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Primary fan relay test:
This is good stuff ain't it! Y'all can send me some money if ya' want.
TIP!!! When jumper paper clips glow fast, and start to smoke, don't hold on to it.
I have no clue where it went either (in the belt area too). I had other things in mind at the time. Like pain.
This is good stuff ain't it! Y'all can send me some money if ya' want.
TIP!!! When jumper paper clips glow fast, and start to smoke, don't hold on to it.
I have no clue where it went either (in the belt area too). I had other things in mind at the time. Like pain.
Last edited by schrade; Jul 18, 2008 at 04:42 PM.
Like my fingers when I let it go an hour ago!
Melting Slicks
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From: Jasper Texas
Sounds like we have both experienced our fair share of pain today. My car popped me earlier, that wasn't so bad. Just a few minutes ago when I was removing the light fixture from my ceiling, somebody seemed to have forgotten to flip the breaker; That one hurt pretty bad!
Safety Car
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From: :45 minutes from everywhere / E-I-E-I-O
Sounds like we have both experienced our fair share of pain today. My car popped me earlier, that wasn't so bad. Just a few minutes ago when I was removing the light fixture from my ceiling, somebody seemed to have forgotten to flip the breaker; That one hurt pretty bad!
We got the primary fan relay plugged into the secondary relay, to confirm that the A-E switch in the relay doesn't work.
This should trip the fan at 119.
Now some of ya's are sayin' your primary fan doesn't come on til 228. That's not what the '94 FSM says, is it? post 114????????????