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I recently sent my out my PCM for a mail order tune from ECS. When I got it back, I had multiple errors populate my DTC (Low fuel, reduced engine power, etc). There is no comm with the PCM and the starter would crank but car wouldn't start. I sent it back and Doug reloaded the tune. Same issues came back and now the starter just clicks. New battery is at 12.6V and only dips 0.2V when the key is turned to start. I'm at a loss here, Doug has been very helpful and has offered to refund my money and tune it back to stock. I would like to eliminate all possibilities before I do that though. I've scoured the forum, but have found no solution. Key notes: I have a 98 base coupe, I have a key resistor bypass, aftermarket sound system and new battery that was drained yesterday. The battery drain has been there since I've had the car. Any help would be greatly appreciated. I am mechanically savvy but don't know a lot about C5 computers. I've checked all PCM fuses and power at the battery and the fuse box, which both check good.
Yeah, I've never seen a charging system fault on my DIC. My battery always slowly drains (a few days), but I also don't drive it much. I don't think it's related to the PCM issue because it was an issue before I got a tune. I guess my main concern is that getting my PCM tuned back to stock won't fix the issue and that maybe my PCM is just fried. I've already spent about $60 shipping it back and forth to New Jersey and if it isn't going to fix it, I might as well sink the next round of shipping costs into a new PCM.
Without seeing the car, all sorts of issues pop up in my head.. Im guessing that you do not have an original Valeo 110 amp alternator.. Anything other than this will give you problems.. without that charging system fault message and a failed system. Im guessing someone bypassed the discreet circuit, You have a sound system that is not very compatible with the tightly monitored electrical system. Anything it sees that is not within the parameters of this discreet circuit throws that fault code.. it was designed in. Not sure why you have a bypass resistor. Not sure if your B+ to the solenoid is tight. This car was Not designed to be electrically modified.
Good Luck
Bill aka ET
I bypassed it so that the car would work after I installed an aftermarket head unit. I had a security issue after installation, that's why I ended up putting the resistor in. Would an issue with the discreet circuit cause no communication with the PCM? How can I test to see if this is a security issue?
I bypassed it so that the car would work after I installed an aftermarket head unit. I had a security issue after installation, that's why I ended up putting the resistor in. Would an issue with the discreet circuit cause no communication with the PCM? How can I test to see if this is a security issue?
The F terminal ( discreet circuit ) is one that goes directly to the PCM with no other intercepts within that circuit. goes from the " Factory Alternator " in this case French made Valeo 110 amp alternator that has this discrete circuit built into it. The PCM monitors the electrical system through this circuit.
First off I’d see if you have a parasitic drain on your battery and take care of that first. Also since you sent the PCM to ECS I’d make sure both connectors at the PCM is secure and wouldn’t be a bad idea to remove the 2 connectors and do a good visual. A quick test to make sure your PCM is “alive” is by checking for a 5 volt reference at the yellow wire at the MAF sensor key ON...you can also check powers and grounds at the PCM. To check your “F” terminal (gray wire) at your alternator you should read anywhere from 2.0-8.5 volts with KOEO or KOER !!...using my Snappy graphing multimeter you see a 0-5 volt square wave...with my voltmeter around 1 volt...remember with a multimeter it only “averages” the voltage !!...also, anytime I see “aftermarket sound system” I think of serial data issues...you get either 12 volts or ground on that data line and there is your no start !!
Thank you for the advice, I'll check these with my lower class voltmeter when I get home. How do I check if the serial data line is the issue? Also, which wires are the power and ground lines for the PCM?
Sounds like you are having a Theft Deterrent Relay (TDR) issue and or a Starter solenoid issue. There is a purple wire on the theft deterrent relay ( The relay is under the passengers dash behind the toe board). The relay is a four relay on the fire wall above the BCM. The color of the wires are RED, PURPLE, Yellow and yellow black stripe.
The TDR purple wire supplies 12 VDC 60 Amps to the starter solenoid when the key is in the CRANK/START position..
Are you getting that voltage on the purple wire when you attempt to crank the engine? You can also read that same wire on the solenoid S terminal.
The GM Solenoids are well known to FAIL. They will not actuate when voltage is applied to them. If you give the starter a good swift THUMP when someone holds the key in the START/CRANK position the starter will usually crank if the solenoid is the issue.
You should also give the wires on the solenoid a good inspection and see if they are clean and tight.
Once you sort out the no start issue, we can attempt to solve the battery drain problem.
Make sure that the battery terminals are clean and properly tightened. The actual GM torque value is 11 ft/lbs for the battery terminal bolts. If you can move a battery cable terminal on the battery by hand, it is NOT properly tightened.
Like Bill mentioned we have to look at a few issues you are having....do you know if the battery was FULLY charged (12.66 volts) when you attempted a start and all you got was a click ??...when trying to start these cars with low battery voltage it can throw these weird codes !!...if it "were" a serial data line issue what you would see from the drivers seat is a "start and stall"...ALL no comms with every module and all your DIC warning messages would be seen as well as your fuel gauge reading empty, your water temp gauge pegging out high and your power windows inop. Below are all the PCM pin outs...just look for your '98 !!
Not really but,,,,,,,,,, If you have a LOW VOLTAGE issue because you have a battery connection problems, that can cause all sorts of issues. YOU MUST insure that the battery is 100% and properly connected before you even start troubleshooting.
Thank you for the advice, I'll check these with my lower class voltmeter when I get home. How do I check if the serial data line is the issue? Also, which wires are the power and ground lines for the PCM?
I responded below with the pin outs if needed !!...also the voltmeter is "middle class"...the 12 volt test light is lower class...the graphing multimeter is upper middle class and the scope is upper class....LOL !!...good luck !!
PS- if the PCM is “alive” you MUST say the following line from this movie...LOL !’
Here's what I found :
When cranking: 11.54@TDR, 12.57@MAF, 0.07@Alternator.
Battery cables are tight, battery reads 12.6V. Security light turns off after three seconds after turning key to on. I'm at a loss. 0.01V on accessory and 9V at solenoid when cranked, 1.7V on accessory and 0.14V when cranked for starter.
Last edited by Chris Scapp; May 14, 2019 at 09:02 PM.
Just tested power at all fuses in my under hood fuse box and the PCM 10A fuse in location 16 is getting no power at all, with key in or while cranking.
First off let’s not worry about the F terminal alternator voltage right now...so with the MAF sensor unplugged and with key ON you are probing the 5 volt ref wire (signal) and you’re reading 12.57 ??...this is the YELLOW wire...you should have 12 volts on the PINK wire..did you check the wrong wire ??...PCM fuse 16 is your ignition supply to the PCM...if you turn the key ON I bet you don’t hear the fuel pump prime...do you ??...IGN1 fuse 45(IP fuse block-next to BCM-hot at all times...this fuse IS for a 98) feeds the PCM fuse through the ignition switch...check IGN1 fuse !!...if fuse good “may” be ignition switch...even with bad ignition switch you’ll see something through the switch !!
Issue after Tune
