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Melange of DTC codes!

T

TurboTahoe

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Hi guys. I could sure use some help. Here's the history:

Over the past month, I've been running into a number of irritating little problems on the Tahoe, all manifesting themselves as intermittent, with the occasional DTC thrown in. The list:

* DTC 44 and 45 - the EGR error codes. Sometimes the codes would be thrown and the truck would lose the wastegate solenoid function, resulting in no boost and lots of black smoke, no power. Very scary on the freeway.
* Action Taken: Replaced EGR Solenoids (both of them), and the vacuum harness (because I broke it when replacing the solenoids)

* DTC 29 - The "glow plug" fault - this was also intermittent, and would cause the glow plugs to not function. The truck would start, but would not glow the plugs.
* Action taken: Replaced glow plug solenoid.

* WIF light - Yes, sometimes the "Water In Fuel" light would flicker on, usually under heavy acceleration. There were times when the EGR codes would come on at the same time.
* Action taken: Vacuumed out the fuel filter, checked filter and filter bowl for water. Cleaned everything out.

* DTC 29 came back, accompanied by loss of glow plug light and no glow activity.
* Action taken: After receiving advice from this forum, I cleaned all my grounds, replaced a faulty one, and put in new 4 ga grounding cables.

* DTC 29 came back... again.
* Action taken: After looking at the schematic and thinking some more, I decided to replace the ignition switch. Did that last night.

Today...

Started and ran normally. No codes, no missing lights, no error lights, nothing. Just ran normally. Went off to work, went to number of meetings, ran some errands... and then... got these codes on the way home:

* DTC 29, 31, 42, 44, 45, 57, 62
* Glows will not glow, but Tahoe appears to run normally otherwise.

I'm really at my wit's end. What do you guys think I should do?

Rob :(
 
OK guys... I thought about it, and decided to check the connector from the ignition switch - where it connects back into the main harness. It was hard to tell if anything was wrong, but I decided to pull it apart a couple of times and then put it back together, in case the issue was either the connector being slightly loose, or dielectric fretting on the connections. (With the most-likely probability being that I had plugged the connector together slightly off, as I installed the ignition switch at 3AM.) I pulled it apart a couple of times (anyone who has done this knows it's not as easy as it sounds) and then put it back together (after disconnecting the battery grounds, of course). All codes are cleared and the truck appears to work properly again.

Just before I did this (just now) it was consistently showing failures, throwing all the codes (shown above) and failing to light the glows. It was consistent even after I cleared the codes - it would just throw them all over again. After wrestling with the connector and reconnecting it, everything appears OK, but given how much trouble I've had the last 2 months, I'm just going to keep a wary eye on it. Argh!

My theory is that the connector was slightly off axis, and driving it around caused it work loose. Unplugging, replugging, and tightening the nut on it has made the connections good again. That's my thought anyway.

Thanks again, I am cautiously optimistic it is gone.

Rob :)
 
I would have said grounds. I have to check mine. WIF is flickering in mine also and the interior lights comes on flickerering randomly. I left the radio tuned to Oral Roberts. I'm hoping it will exercise the demons.
 
Acesneights1 said:
I also put oil of olay in the crankcase hoping to make my 95 into a 98 or 99....:)
Click to expand...


i believe i was told to turn the radio to oral roberts and do the above as well when i was having my demons in the truck. but since i've bought a good amount of upgrades it seems the demon is on my side now and we are getting along great. :devil::reddevil:
 
TurboTahoe said:
3 days and no more codes... I'm still holding my breath.

Rob :)
Click to expand...

Spoke too soon!

ACK! The codes are BACK!

* DTC 29, 31, 42, 44, 45, 57, 62
* Glows will not glow, but Tahoe appears to run normally otherwise.

I just checked the connections to the ignition switch, and it looks good. I'm stumped.

Anyone have a good idea?

Rob :)
 
DTC 29 - Glow Plug Relay Fault
DTC 31 - EGR Control Pressure/Baro Sensor Circuit Low (High Vacuum)
DTC 42 - Fuel Temperature Circuit Low (High Temp)
DTC 44 - EGR Pulse Width Error
DTC 57 - PCM 5 Volt Shorted
DTC 62 - Turbo Boost Sensor Circuit Low

That's a strange combo, but it is consistent. What do you guys think? I could really use some help here..

Rob :)
 
Thanks Tim. That's brilliant. I will do so and let you know the result. You know, the 'other place' is really really empty without you and GMCTD and Kevin around. Just not the same. I miss you guys!

Will advise.

Rob :)
 
No need to miss us we are here, I have a real heart ache the way that place was sold, and volunteer work given freely by myself & others made/makes a huge profit for owners old & new, I won't be back there is all I have to add.
 
1. Voltage does not drop at all when glows light. Hardly even drops when I crank the starter.
2. If I clear the codes, the codes come right back if I start up - glows don't work (but weather is warm, so truck WILL start).
3. If I clear the codes AND WAIT FOR THE TRUCK TO COOL OFF, the glows work and all codes are gone.
4. If I do start the truck when it is coding, it throws codes immediately. In fact, the SES light stays on, and the glows never come on, and I get all the weird codes.

I agree, it sounds like grounding gremlins. The only curious thing is the possible tie-in to temperature.

I will go back over my grounds and see if I find anything else.

Thanks for the encouragement and suggestions,

Rob
 
Turbine Doc said:
There is an intermittent gnd somewhere, or voltage is dropping really bad during the glow cycle, reset codes, pull glow fuse and see if the only one after that shows up is glow related
Click to expand...

Results:


  1. I reset codes and pulled the glow fuse.
  2. Moved key to 'run' position - noted that glow plug light was off.
  3. Started engine - SES light stays on. No problems - cranks quickly.
  4. Removed ignition key, shut off truck.
  5. Checked for codes - DTC 29, 44, 45
  6. DTC 29 - Glow Plug Relay Fault
    DTC 44 - EGR Pulse Width Error
    DTC 45 - EGR Vent Error
  7. Returned glow plug fuse.
  8. Key to 'run' - No glow plug light, SES stays on.
I'm stumped. I wonder if I have a bad glow relay? I just replaced it. Could it be a thermal problem, or is it back to grounds? I'm going to re-check grounds.

Rob :)
 
Still looking like a gnd issue Rob, you can check the relay though, take it off the truck and put 12V to the control coil, then with meter see if you hi resistance to the load side of the relay, you can do same in truck as well just remember the input load side of the relay is always hot, even with key off so disconnect from the underhood fuse center, never heard of it but a thought just occurred to me, that wire to the relay is main power, if internally corroded it could cause a pretty healthy voltage drop, so check it's resistance also.

Your code 44 & 45 are common to each other in talking to the PCM, on S engines PCM monitors position to "control" EGR flow, I'm suspecting the gnd for those is in play here, I'll have to look around the manual schematics after while to see if I can find where that common gnd mite be.
 
Checking connectors... So far all I have found is a broken glow plug wire. However, the way it's waving around loose (rear-most on driver's side) I'm wondering if it has been shorting out on things down there. Looks like a new connector AND new glows are in order, at a minimum. I'm still not convinced this is the end of it, however.... Any suggestions are welcome.

Rob :)
 
OK, Thanks for listening!

Just did the following:


  • Fixed broken Glow Plug wire
  • Repaired "questionable" ground from body to frame - I worked on this ground before, so it's clean and new, but if you look at the ground point from body to frame, it connects to a 'threaded stud' on the firewall. It is secured using a nut-washer and nothing else. It was a little loose, so I decided to make a 'connectivity sandwich'. I spun a 6mm nut on the threaded stud, then the new 4 ga ground cables, then a lock washer, then the nut-washer, and snugged the whole thing down
  • Also disassembled the frame ground, inserted lock washer, and re-assembled.
And then... the nasty part. I bought AC Delco 60g glows and replaced all the plugs. I wonder if these crusty old 9g glows were the originals? Just finished the messy job. Because of the 3" body lift, I did need to drop the flexible splash guards and the downpipe to get to all 8 glows. The hardest ones to get to were the ones on the passenger side in-between the exhaust manifold runners.

Here's a picture of them - I think they are the original 9g glow plugs. Nasty looking, eh? As you can see, a couple of the flag terminals just fell off. I'm very thankful none of these plugs were swollen. They all came out easily. The 60g glows also went in easily. I did buy a packet of new female spade connectors, and replaced most of them, but they don't seem that robust in construction.

BTW, does anyone know where you get replacement glow connectors (i.e. factory style)?

Used-9g-glow-plugs1.jpg


Used-9g-glow-plugs2.jpg


Used-9g-glow-plugs3.jpg


Sadly, I still feel I haven't found the root cause of the melange of DTC codes. Time will tell. These intermittent electrical problems are terribly hard to pin down.

Any sage advice is solicited.

Rob :)
 
Last edited:
Awful shy on "sage advice", my friend... so far, you're doing everything I would do. Eliminate stuff one at a time.
 
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