Intermittent starts, runs, then no starts no crank??

netbyte

Original poster
Member
Jan 15, 2021
9
Molly3991!
Have a use LT 06 TB, and it likes me one day and hates me next. Bought it a week ago and now can not find out why it's so intermittent. Have checked all the fuses, relays, and replaced today, with new parts, the TBS sensor, ignition switch module, Safety/neutral switch, manifold sensor, shift cable, and new battery. When its decides not to crank/start I get the wrench/4 axle light and the dash battery gauge only reads about 7 volts. However the new battery at the terminal reads 12 plus volts. The wiring does appear to have seen some troubleshooting, as some of the cable plastic covering are removed. The TB has totally lost all power while driving, and had to be towed.

During its brief running time I have seen lots of codes PO 171, PO300, P2122, and even a p1400. The 2122 cause me to replace the TBS. I believe there are no stored codes at this time. Don't understand why I get the Wrench/Axle warning light and the low voltage on the gauge, during the no start no crank (jumpering the start relay 87-30 cranks the starter), but will not start. After the no start/no crank there are no stored codes? Appreciate any insight or information on additional troubleshooting suggestions. I have a limited code reader, but good DVM.
Thanks
 

gmcman

Member
Dec 12, 2011
4,656
Have you load tested the battery?

What is the voltage when the engine is idling? Use a multi-meter, not the dash gauge.

If the battery checks out, then it almost sounds like a bad battery cable. Remove the NEG first and check, then POS +, look for the tabs inside the connectors that contact the battery terninal.

The battery might read 12V idle, but under load it's a different animal.

Just because thee cables are tight, doesn't mean they are making good contact.

Also check the chassis grounds.
 

netbyte

Original poster
Member
Jan 15, 2021
9
Molly3991!
Thanks for your reply and battery advice. New Battery tested good under load, I also installed new battery cable bolts, and sanded the ends of both cables. Checked cables for corrosion and all tested and looked good.
Checked all engine and chassis grounds and tighten them and verified continuity.
Today after installing 6 new 41-103 plugs, and removed the incorrect 41-110 plugs, amazingly, the truck started, and so far no codes??
Went a on long drive, 100 miles or so, stopped several times and truck restarted fine. Hopefully with all of the new major parts, it will continue to do well.
Thanks again for caring and to share your experience and advice.
 

netbyte

Original poster
Member
Jan 15, 2021
9
Molly3991!
Well it's gotten even worse, after having Igor towed several times due to the same problem. I'm on A new path. After the last tow, due to total loss of power, totally disassemble fuse block and removed all of the PCM connectors, and using compressor, blew out the items and PCM pins, and harness connectors.
Tried to start and truck briefly fired and died. My son said he wanted to try something and ask me start car. Turn key to start and fired right up???? All he did was push on the PCM cables and wiggled the whole engine wiring harness.
Did gets several engine lights lit up and the truck now has power and starts, and if not bang, on the PCM cables and it fires every time.
Lesson learned is troubleshooting the PCM cables and wiring up to the PCM and other components does not always find your problem!
Strongly believe my problem is engine harness connectors or pins on PCM related.
Just wanted to share some old fashion shade tree mechanic problem solving experience
Thanks
 

netbyte

Original poster
Member
Jan 15, 2021
9
Molly3991!
Thanks for your reply and yes the switch was the first item replaced.
The truck can be started by moving the C2 wiring up or down or around. Car starts right away, when someone turns key while wiring is being moved around. The C2 connector is missing the locking shell around the connector?? My problem is clearly engine wiring harness/connector related. However when moving the cables around I also lose 4x4 lights, and no 4x4 servos. BPIA, as the this TB is the fully option one, and regular engine wiring harness may not work?
Thanks
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
I would closely inspect every terminal pin and mating pin in that connector. Get some new pins, do a pin drag test, etc.
 

netbyte

Original poster
Member
Jan 15, 2021
9
Molly3991!
I would closely inspect every terminal pin and mating pin in that connector. Get some new pins, do a pin drag test, etc.
Hey TJ
Excellent advice and I'm on the same path. Can not find PCM pinouts for the 2006 trailblazer? Repinning sound challenging, but I did find a replacement connect and pins for the C2.
Have already done the fuse block disassembly, and no broken wires detected. Leaning towards the connection at the PCM, but want to ohm out the PCM connectors/wiring as my next step.
Appreciate your reply, thank you.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
You can find a complete set of diagrams in the service literature found in @Moosemans signature.

I have attached a page from that literature here showing the C2 connections.
Given that the truck starts when this connector is wiggled (right?) one could look over the functions of each of these terminals and compile a list of likely suspects, ruling out connections that would obviously not impede startup. Most critical might be the PCM ground connection in C2?

Edit: pdf attachment failed

Screenshot instead
Screenshot_20210222-101341.png
 
Last edited:

netbyte

Original poster
Member
Jan 15, 2021
9
Molly3991!
Just what the Dr ordered!!!!Much thanks will get on the DVM stuff today. I know it's a darn connector or wires, so the solution should be discoverable, with time. This project has been all consuming due to the intermittences of the failure. One day fine everything works, truck starts runs fine, then totally loss of power and the NS,NG all over again
 

netbyte

Original poster
Member
Jan 15, 2021
9
Molly3991!
Just what the Dr ordered!!!!Much thanks will get on the DVM stuff today. I know it's a darn connector or wires, so the solution should be discoverable, with time. This project has been all consuming due to the intermittences of the failure. One day fine everything works, truck starts runs fine, then totally loss of power and the NS,NG all over again
Hey TJ
Great info and in DVM'ing out the pins, the ppl/wht on pin 48 (C2) goes where? Guess I just need to do more studying of all of schematics.
Checked fuse block, two ppl/wht wires on C1 and the ppl/wht on big 40 pin connector on side of fuse block? Schematic pin 48 on c2 goes to pin 21 on something or has the problem surfaced?
Not really sure what the HO2S hi sig sense 1 is all about
Thanks for all of the great advice and pointing me in the right direction
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
You need to get the full set downloaded as previously mentioned. There you will see that the "21" is not a pin on another component but a simple reference number to be continued on the next page! You follow those references from page to page and end up learning that HO2S is a Heated Oxygen Sensor.
 

budwich

Member
Jun 16, 2013
2,027
kanata
Just what the Dr ordered!!!!Much thanks will get on the DVM stuff today. I know it's a darn connector or wires, so the solution should be discoverable, with time. This project has been all consuming due to the intermittences of the failure. One day fine everything works, truck starts runs fine, then totally loss of power and the NS,NG all over again
what does the last part actually mean... NS,NG you need to describe what you are seeing at that point in terms of dash indicators, gages AND reactions to the key sequence for a "NOSTART" conditions. Although you indicate the C2 connector, it does not really appear that those pins / signals would directly cause a nostart condition although you need to describe that condition better... does the engine turn over or you don't even get any noise happening. My guess right now, is you get engine turn over but never get any "firing". IF so, you can double check that with spraying in some start fluid when the NS happens (it sounds like you can create it... hopefully). If it fires, then you have potentially some fueling related condition. Based on the C2 "observation", it is possible that the TAC MTR signals are a problem which I do believe is related to throttle control... check that.

Another possible one is the cam pos solenoid.
 
Last edited:

netbyte

Original poster
Member
Jan 15, 2021
9
Molly3991!
Thanks to all whole tried to help out
This has been the greatest challenge to limited troubleshooting skills
The NSNG is no start no crank but also complete loss of power to dash, dome horn, 4x4 sw and windows
Jumper the starter relays gets a cranks and when jumping reply next to it get a quick start then dies
Yesterday took apart the fuse bock for the 4 time, re cleaned the wired inner board with contact cleaner again, air blew all FB parts
Reassemble and installed all relays and fuses, connected everything up!!
The damn thing fired right up and no codes , no WIL
Still have no clue what the real problem was/may have been but for now it’s starting and running great
This a great bunch of very knowledgeable people and are truly a bright light when in the dark deep end of the pool
Thanks to all
 
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budwich

Member
Jun 16, 2013
2,027
kanata
glad you got further and have a working vehicle. Hopefully, it won't come back to haunt you again. Looking further at the C2, the other two pins that are more likely related to your problem (nothing on the dash) is the KS pins which I do believe deal with "key detection" meaning that the system sees that your key is in the ignition.... I think. So if those are poorly connected then you might not getting any start operation along with some other things not happening.
 

netbyte

Original poster
Member
Jan 15, 2021
9
Molly3991!
Great bunch of very experienced people. THANKS AGAIN for sharing your knowledge and suggestions. After getting it running and no codes or WIL's decided to let the 06 go. I did the right thing and posted the no crank no start problems and really reduce the selling price.

But the really good news is I picked up a super clean all original, one owner 2002 Trailblazer LS 4x4 with the g80, block heater (really in Arizona) and a few other off road things. Its like brand new never really used with only 68k miles. Best of all its starts every time !!!! Very happy Trailblazer owner here
 

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