H3 Electrical gremlin after PCM enhancement

I purchased a used pcm and sent it off to get a tune added. Once it arrived I installed it. First issue I had was during case relearn I received an error saying the tech2 lost connections. I figured I must have accidentally bumped the connector as you must put one foot on brake and one on accelerator. Restarted process and completed with no issues.

i then took a long (200 mile) test drive to feel the performance improvements and give the obd a chance to run through self diagnostics. None of the test ran. Also while driving the radio turned itself off for a few seconds then back on several times. After the second time I kept an eye on the dash to see if anything else was going on. I noticed that when the radio, whether on local Channels or xm, went off it appeared to loose complete power (no clock). When it comes back on it always reverts to fm band. The radio also retained all of the channels programmed and correct time though.

Also while driving I left the actron scan tool on to watch live data and drive cycle monitors. Multiple times it would loose connection with obd requiring me to restart tool. It is powered by obd and never lost power, just connection with CAN bus.

When I got home I put the stock PCM back in and everything is back to normal. Poor performance, shift points and all. No gremlins.

I contacted tuner to talk about issue. I figured that I must have bought a bad second hand PCM (tried saving a few bucks) so I ordered one from tuner and he put the tune on theirs for me then mailed it out. Once it arrived I installed that one and same issues as before.

After driving several days of the obd self test have all run except the evap The only codes I have been getting are “U” codes. The more I drive the less codes I get but radio continues to appear to lose power. Any ideas on how to resolve. Anyone else run into this after pcm tune. 2007 h3 i5 and never had issues before and still have no issues with stock pcm installed.

Also so as an FYI I ran every test that tech2 has and everything on bcm, digital radio module and radio module show all good with no codes or issues.

Your issues sound like battery terminals! Check those just for good measure

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Radio works but with tuned pcm installed, I have two with same tune, it acts up. Put stock pcm back in and no issues. (I have total of three pcms now). One of the tuned pcms I bought from junkyard and one came from tuner. The radio works but intermittently acts like it looses power then comes back on. May drive 50 miles before it happens and then might happen again within ten to fifteen minutes.

Battery terminals are military grade after market and are good.

When I talked to tuner he thought maybe I had a bad connection on the communications side as all the codes were communications related.

I dont know tuning. Is there something in the tuning of the pcm that could conflict with DSM or BCM? The issue appears to be on that end but only happens with tuned pcms are installed.

I went ahead and checked for codes again using tech2. All is clear on pcm but found these on bcm. Keep in mind with stocked tuned pcm I don’t get these. I have looked each up but can’t find anything on trouble shooting each

U1137 lost communication with satellite digital audio reception system
U1151 lost communication with onstar
U1016 lost communication with engine control system
U1064 lost communication with body control module
U1128 loss of IRC communication

I am now thinking maybe one of the three plugs on pcm is not making a perfect connection. Any clue on which one I should tear into and any suggestions on how to remove black plastic cover on plugs to check wires?

Bruces said:

I went ahead and checked for codes again using tech2. All is clear on pcm but found these on bcm. Keep in mind with stocked tuned pcm I don’t get these. I have looked each up but can’t find anything on trouble shooting each

U1137 lost communication with satellite digital audio reception system
U1151 lost communication with onstar
U1016 lost communication with engine control system
U1064 lost communication with body control module
U1128 loss of IRC communication

I am now thinking maybe one of the three plugs on pcm is not making a perfect connection. Any clue on which one I should tear into and any suggestions on how to remove black plastic cover on plugs to check wires?

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I was thinking you had some kind of issue like this related to the bus. Get some electrical cleaner/ spray alcohol and give it a good spray. Get some canned air to blow it all out. Check to see if any of the terminals have recessed into the plug. Get one of those lighted magnifying glasses to go over it real well. I had thirty years of experience working with circuit cards. This is just another type of circuit card. Plug it in, unplug it. It's a way to make better connection with the terminals. Do it several times and then see if what happens. Basic circuit card troubleshooting before you break out more involved test equipment.

I don’t want to speak too soon but I think I may have figured it out. On the gray plug (c3) on the inside is a small green tab that broke off and fell on top of the rubber ring. This prevented the plug from seating on the bottom pins. Pulled the broken tab out, reseat the rubber seal and reinstalled the pcm. Radio did not lose power on 40 mile drive. I will take it out again to see how it does.

That’s probably the issue. gfbh3t had a similar problem after re-flashing his pcm. Eventually he gave up and bit the bullet for a new one.

GMs connector design is very poor, and clumsy to use. It seems way too complicated given the simple task it does. Several times I have found gremlins related to bent pins on the connectors...particularly on the bottom side of the fuse box. The plug goes on and latches...but one (or more) pins gets bent over instead of going into its hole.

GM is not alone in a problem like this with connectors. You can't be heavy-handed with these connectors of any type. The same problems happen with connectors like this that are not auto industry related. I'm glad that the problem was solved with a closer inspection.