Hello all,

Had a wonderful intermittent (now seemingly permanent) issue present itself over the Christmas holidays. Car is an '04 C5, auto, ~150k, longtube headers, ECS tune.

Several days ago I ran a quick errand in the morning and the car drove fine, went to drive it again later in the afternoon and the car just cranked and cranked but never started. Cranking sounded healthy, wasn't struggling or slowing down from dropping voltage. The next day I was troubleshooting some, wouldn't start at first but after another try it fired up immediately so I couldn't really troubleshoot anymore. Drove fine the rest of the day and all the following day (several hours of driving) with no issues.

Went to drive it again on Christmas Eve, would not start again. Just kept cranking and cranking, this time had a couple small backfires. The car was in the garage so I wasn't sure if it was out the exhaust or out the intake but I believe it was the exhaust. I let it sit overnight, tried to start it yesterday and again today and no dice. Just constant cranking but no firing. I pulled the following codes from the DIC:

-- PCM
- no codes

--TCS
- U1016 H

-- SDM
- U1016 H

-- IPC
- B0516 H
- U1016 H

-- LDCM
-U1016 H

-- RDCM
- B2203 H
- B2283 H
- B2287 H
- B2285 H
- U1255 H
- U1064 H
- U1016 H
- U10996 H

-- RFA
- U1016 H

The abundance of RDCM codes had me thinking it might be related to a short in the wiring, but wouldn't that cause the car to not even crank at all? I might be mistaken on that, but I figured a security fault wouldn't allow the starter solenoid to cycle. Regardless, I tried opening & closing the passenger door multiple times as well as jiggling the accordion and the harness within but the car still didn't start.

I felt around to the grounds I could see in the engine bay and they all seemed tight, nothing loose or damaged. Over the weekend I plan to get underneath the car and try to inspect the wiring around the starter and crank position sensor - basically any wiring that's around the headers to see if anything might be burnt or melted, but I tried to tuck them out of the way as much as I could during the install so I'm not sure that's it. Would a failing cam or crank sensor cause a crank no start situation, with no codes thrown?

Any suggestions or pointers on things to check are greatly appreciated. I have a volt meter handy but honestly my knowledge of how to test certain connections or components is very minimal, so any extra help there is appreciated as well. Thanks in advance!

 

Hello Mr. Heisenberg !!...did you ever get that fuel pump fuse issue fixed a few months back ??...if not I'd look at that fuse....Yes, a bad crank sensor and or crank sensor wiring issue would cause a "cranking no start".Does the Tach appear to move during cranking ??...well the first thing I'd check is if you're getting any spark during cranking (if no Tach movement probably no spark)...if good spark then give the intake or a vacuum line a good toot of Brake Kleen and see if it starts...if it tries to start or starts you have a fuel delivery issue...you can start there. I remember you said you just have a multimeter. You had a bunch of "U codes" also...do these easy things and maybe move on to the CAN network. If you can wait a few years when I retire to SW Florida I'll come over and help...LOL !!!...and I "THINK" in 2004 GM went to the GMLAN network but not 100% sure...that has a low and high speed bus !!

 

With no codes I would start with fueling.

 

You Guys still in Cream Ridge ??

 

Thanks for the quick responses guys! Rwobs777 no I never reached a resolution to that prior issue. It would only ever happen after long drives and hasn't happened since. I've had a busy few months with work and moving etc, so it's been on the backburner, but I will get around to it eventually.


In regards to fuel, I can hear the pumps prime for a few seconds when turning the key to ON, and despite not having a fuel pressure gauge to see the actual pressure, when I press the schrader fitting fuel does spray out, so I have some pressure there at least. Also after cranking I can get a bit of fuel smell from the exhaust.

When I tried cranking it again just now, the tach does NOT move at all. So it seems like from these couple tests I am getting fuel but I'm not getting spark..

 

I had a dead C5 for about 3 months. Cranked fine and threw a P1518 code pointing to the TAC module. Traced out wiring and could not find and broken wires. Got another TAC and symptoms stayed the same. Finally disassembled the console and dash and removed the Ignition Switch and replaced the rear electrical plastic part with a new OEM Delco part (D1499C). Car started immediately and no codes were stored. May not be your problem but low voltage can cause many strange things including codes. Ignition Switch was much less expensive than the TAC which was pointed to in the Service Manual. Good Luck finding the culprit.

 

The way I would diagnose this is to check for spark...do you have a 12 volt test light ??...connect the 12v test light to ground and remove a spark plug wire at the coil pack and when the car is cranking see if you have spark from the coil pack...if that's good now look at fuel...you can get a cheap pressure gauge at Harbor Freight if there is one near you...if not try Manny, Moe and Jack or Auto Zone....now check fuel pressure KOEO...(my 2001 is 55-62 psi) ...I don't have the exact numbers for your year....if pressure is good then look for injector pulse...you'll need the 12 v test light again....disconnect an easy injector...connect the test light to the NEGATIVE battery terminal ...touch the tip of the test light to the wire with KOEO on the injector that is the same color wire on each injector….the wires that are the same color on all injectors are your 12 volt feed...test light should light...now connect the test light to battery POSITIVE....while CRANKING touch the tip of the test light to the other wire (striped)...the test light should flicker DIMLY letting us know the PCM is grounding the circuit opening the fuel injector....if you have NO spark OR injector pulse it could be the crank sensor...I just helped a member last month that had the same issue of a "cranking no start" and after he replaced the crank sensor with an OEM one it still didn't start...we determined he had low voltage (3 volts) instead of 12 coming from the PCM...(YOU MUST ALWAYS CHECK THE WIRING !!)... we checked PCM power and grounds and all were good...I'm waiting to hear the outcome...testing the crank sensor wiring is a little more difficult not really in the procedure but where it's located !!

 

Same location, new shop though.

 

My '01 has just a Blackwing CAI and Borla exhaust with X pipe...worth a tune ??...if I did decide can I just bring the car instead of removing the PCM ??...are Monday's good for you guys ??

 

Thanks for the info. Today I put the front of the car up on stands and climbed underneath to check the wiring I could see. All the wires around the starter seemed just fine, no cracking or melting or anything really. They don't look any worse than when I was underneath it a few months ago. I was able to reach G104 on the side of the block with a long screwdriver and it seems tight. All the wires on the starter seem tight as well. There's some surface rust on the post and nut, but still tight. I could only see part of the wire for the crank sensor but just like above, it looks the same as before. Nothing visibly wrong with it (I know visual inspections only say so much, but I at least wasn't able to see any cracks or damage).

I don't have a test light unfortunately but from trying to crank again I'm getting a strong fuel smell from the exhaust, so I believe the injectors are firing. With KOEO I checked fuses 16, 18, 22 and 23 and they were all good, only maybe .1v lower than the battery.

I also did a little searching and per your thought on a serial bus issue I came across this thread, so I pulled the harnesses out of the passenger door and checked the wiring and connections. None of them appeared damaged and the male and female pins seemed okay, nothing that would indicate a bad connection.

Next I planned to check for spark but a couple relays under the hood started clicking and buzzing, went to turn the key off and noticed the Charge System Failure message. Checked battery voltage and it was low (12.1v), probably from KOEO and cranking several times. So I will have to wait until the girlfriend gets home from work to jump/charge it and continue testing.

NOTE: a big reason I checked the door harnesses again is because the first time this happened, my girlfriend had just gotten in the car as well. Went to start and just cranked, no start. As mentioned in my original post I let it sit overnight, when testing the next day (after trying to jump it with her car i.e., battery at proper voltage) it would crank and crank and not start, but when I opened and closed the passenger door ONCE and tried cranking again it fired up immediately. Drove it for a few days with no issue and without opening the passenger door at all. Christmas Eve is what stranded it the last time which - as before - was when the GF got in the car again. Except this time, opening and closing the door did nothing. Could this be a bit more indicative of a serial bus issue? Maybe it's just a coincidence? Maybe my girlfriend is just bad luck? I want to test this thoroughly again once I can get the battery up to proper voltage, but also curious of your thoughts as well.

The front of the car is at least up on stands and ready to continue troubleshooting, which is half the battle! Such a PITA getting a jack under this thing, and a low-profile jack at that! Had to push it up onto some wood planks just for the jack to barely fit. But at least it looks good!




As always thank you everyone for the help. Sorry I wasn't able to report back with more now but at least I was able to check a few things.

 

 

So I actually did try that too, mine has two splice packs so I removed the shorting bar from the one with only four wires but it still wouldn't start. Perhaps the battery was still too low to actually start, I'm not sure. I wasn't aware of jumping the light and dark green wires so maybe I'll try that next. So if I'm understanding correctly, if I try this approach and the car still doesn't start, we can rule out a serial bus issue?

 

So I'm assuming your '04 has the old Class 2 Data Network and not a 2 wire GMLAN ??...yes, if it didn't start with the shorting bar removed on the C2 connector do the same thing with on C1 but jumper the dark and light green wires....PCM and BCM must be on the network for the car to start...I enclosed a pic of mine being jumpered and it started right up !!...if it still doesn't start maybe PCM or BCM issues

...helps to have a CAN breakout box and lab scope to troubleshoot these issues !!

 

Update: so today with the girlfriend's car running and jumper cables connected, I had her crank while I checked for spark. I used the screwdriver method and tested the front most plug on both the drivers and passenger's side and didn't see any spark from either. Still a strong, fresh fuel smell from the exhaust so spark is what's missing.

Next, I used your method pictured above and jumpered the light and dark green wires. Tried cranking again, no dice. Just cranked and cranked and never fired.

 

 

 

BigHank suggested checking the ignition switch. I had the same symptoms you seem to be having. No codes, crank but no start, no detectable spark. Bought a crank position sensor and a new ignition switch. New crank sensor is still on my workbench in the original box. Old ignition switch is in the trash and my car starts without issue. Just sayin..... YMMV

 

 

Thanks for the extra suggestion - I'd done some reading on this issue and most of the threads I came across mentioned a code as well so I didn't prioritize it yet. But since you mentioned you didn't have any codes, I just went out and tore the dash apart to remove the switch from mine. I cleaned all the pellet contact locations (there were several 'burnt' ones), reassembled it and plugged it back into the car, but still no start. Cranking sounds a tad better, but still wouldn't fire.


Thanks for the instructions, I'll pick up and/or make a test light and check these out.