04 Grand Am No Start, PCM, BCM?

JAZAuto

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04 Grand Am (83K) with 3.1L will not start. I know from troubleshooting that the PCM computer is not grounding the start relay. I also know that the BCM must not be working because the keyless entry fob quit working at the same time. A scanner check shows that the PCM is not responding to the scan at all. Battery voltage OK, all fuses checked and the igintion switch seems to activate all the correct circuits in the "on" and "crank" positions. The fuel pump comes on for the required 4 seconds when the key is turned on but that's it - no clicks or noise in the start postion. This model does not have a passkey.

I'm guessing that the BCM is blown which necessitates a dealer fix (reprogramming, etc). But I don't have a full schematic to see how the BCM can inhibit the PCM and prevent the start signal to the start relay.

Anybody have any ideas? Does anyone have the exact schematic showing the ignition switch wiring and the power lines going to the PCM & BCM?
 

jasonn20

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What in the world did you do to cause these problems ?? :ROFL

But anyways you might have a bad neutral safety switch. Try putting the car in neutral and see if it starts.
 

Gus

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You are making a lot of assumptions here....If the fuel pump runs, it is being turned on by the PCM...

It doesn't have PassKey, but it does have PassLock.....

When you turn the key to the crank position(no crank), what happens to the THEFT light when you release the key to the on position? Does it flash?

What kind of a scanner are you using to check with the PCM?

Do you have a scanner capable of communicating with the BCM? If yes, are there any Theft Deterrant codes set?

Have you checked your battery terminals? Clean and tight? Good charge?

Have you checked for power at the "S" terminal with the key in the crank position?

Remove the starter relay, with the key on, check for power with a test light attached to ground, in the four legs....if you have power on 2 of them, the 40A fuse and the neutral safety switch are ok....if only one, then check the neutral safety switch, ignition switch, and the PCM ACC fuse.......
 

JAZAuto

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Thanks guys for the comments so far. The shift switch is something I haven't considered. I will try shifting around to neutral to see if that changes anything. I haven't noticed any "theft" lights coming on but let me be me more observant during a crank attempt. Battery voltage measures 12.6 anywhere I check and the headlights are bright. I am not near the vehicle tonight but will report back.

To respond to Gus, the starter relay coil is not energizing on "crank" because the ground end of the relay coil is not grounding, as this ground comes from the PCM (according to my 3800 diagram from my other GM cars) The (+) side of the relay coil measures good in the relay socket. That's why I know the ignition switch (Hot in Run, Bulb test) and fuses are good. Also, the crank fuse also lights up nicely with a test lamp when the ignition moves to the crank position, and this feeds into a different terminal (crank sense) of the PCM.

My "scanner" is actually just an AutoXray 2000 code reader (I know, yuk) used to maintain the 5 cars in my family (and the inevitable boyfriend/girlfried extensions that come with a large family). But why the reader acts like the computer is dead is scary. (It says "vehicle not responding-are you sure the ignition switch is on?") The reader still works on my other cars. There is a "data link connector" fuse but I checked it both visually and with a test light, as I did basically with all the fuses on all three sides of this vehicle.

I wouldn't think a bad neutral safety switch would inhibit the communication to the diagnostic connector, but maybe I'm wrong. I'll post what I find next.
By the way I heard that sometimes the BCM gets water in it from the heater core compartment and does strange things to the car, but I checked and everything is dry. :-\
 

JAZAuto

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UPDATE:

Well, the neutral switch check didn't affect anything during start attempts.

No indication of a "security" light at any time except during the bulb check (all idiot lights illuminate then)

Also I checked at the diagnostic connector for grounds and (+) voltage where they should be (according to my Chevy Venture 3.4 manual) and it checks OK but as I said still no communication with the code reader.

Noticed the following that should really point to something, but I'm not sure what:

When ignition is in the "on position" the gas gage does not move up even though the tank is half full.
Also, if I switch the high beams on the outside lights respond - but the "high beam " indicatator light stays out. (but it does come on during bulb test).

Help!!! Any ideas?
 

NickD

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Prefer the words , no crank, no start gets confusing. With that kind of problem, first dig out my remote starter switch and hit the starter solenoid directly. If it cranks and really sounds healthy, start tracing back, if not, can be any of a number of problems. A typical one is corrosion between the starter and the bell housing, sounds weird I know, sucker is bolted in tight, use a voltmeter to check for high voltage ground drops. If all that is good, can be the starter itself, GM is no longer making those reliable rebuildable cast iron jobs, all cheap tin with a cheap tin solenoid sealed like a pop can that costs two bucks to manufacturer, you won't find that price at your dealer. Starters are throwaway today.

Check that first, takes a couple of minutes, then work backwards.
 

jasonn20

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CHeck everything on the car and find the things that do not work (brake lights, hazard switch, cig lighter, radio, power seats, etc...) make a list test everything

The PCM and BCM usually do not go bad without a reason. Is everythong original on this vehicle (radio, keyless entry etc...)

There is a fuse panel underhood and under the kick panel if you were unaware. Fuse 5 and 54 underhood then fuse g under dash

Has this car been wrecked, flood damage, or anthing else that might need to be added to the story?
 

JAZAuto

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Where is fuse "G" ? I know of side dash left, side dash right, and the underhood relay/fuse box. Is there another bank somewhere?
 

NickD

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Gee, if the starter doesn't crank, check the starter, glad I am not paying you 85 bucks an hour.
 

JAZAuto

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Well, I was trying to avoid the $100/ hr dealer that's why I'm tinkering with it in my "spare" time. I want to donate to this site but it sounds like the dealer is going to get $$$.

Here's a recap:

04 Grand Am - 83K miles -NO CRANK
The car was driven to work with no prior problems and after work the car was "dead" - no crank, no click.

THINGS THAT WORK:
The battery is fine. Jumping (+) to the starter "S" terminal pops the solenoid. Voltage 12.7V. Lights are bright.
Manual power door locks are OK.
ALL three fuse banks have had every fuse checked.
ALL idiot lights come on during bulb check.
The fuel pump runs for 2 seconds in the ON position.
The security light stays off other than bulb check.
All accessories work that are supposed to work in the ON and ACC position. (except as noted below)
It has an aftermarket radio but this was installed before we got the vehicle a year ago.

WHAT DOESN'T WORK:
The key fob remote for door locks and trunk lock doesn't work.
The PCM is not grounding the start relay during crank attempt. (my test)
THE DIAGNOSTIC CONNECTOR DOES NOT RESPOND AT ALL TO A CODE READER. (Power and Ground terminals at diagnostic connector check OK)
The gas gage stays at "0" in "ON" even though the tank is half full. No prior gas gage problems.
If the bright headlights are activated the dashboard indicator stays dark but the headlights work OK.

A weird grounding problem somewhere? Or a bad PCM/BCM/theft module and let the dealer handle it and my money?
 

NickD

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Could post a circuit of the starter circuit, Jim. Like on my DeVille anti-thief circuit, open relay contacts in series with the starter solenoid circuit prevents cranking the starter, that can be bypassed, but would have worry about someone stealing my car. Could be the same problem here. Don't know until you see the circuit.

Did you say you can manually engage the starter? Do that all the time when working on an engine with a remote starter switch, engine starts with the key in the run position. Want to be awake when doing that, transmission in neutral, wheels blocked, parking brake on hard.
 

NickD

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If the starter relay contacts close, starter motor should run, the solenoid of this relay has the high side connected to the neutral safety switch with the path complete in the P or N positions back through the starter contacts of the ignition switch. So with the ignition switch in start position, gear in park or neutral, 12 volts should be measured at the top of the starter solenoid.

The lower part of the starter solenoid gets tricky, it's going to the PCM looking for a ground that it apparently gets if the left side of the ignition starter switch applies 12 V to pin 23 of the PCM that either activates a relay in the PCM, but more likely a NPN transistor. If this is the problem, you would be measuring 12 V at the low side of the coil with someone holding the ignition switch in the start position, could either be a fried transistor or something else is preventing pin 76 from grounding, like the anti-thief device, that would be yet another circuit to look at non shown in this diagram.

The yellow wire connected up to B2 could be cut and B2 directly grounded that would completely bypass the PCM as the top side of the starter relay is still controlled by the ignition switch. Or you have to dig deeper into the anti-thief circuitry to find the missing link. An alldata.com subscription or a shop manual would certainly help. Without the rest of the circuitry, I am dead, Gus certainly could help as he has access.

I have been fuel sender problems with the introduction of ethanol fuels, this is the last fuel sender I have pulled.
.

And always problems with remote entry, recently found it was cheaper to buy the entire kit with a new receiver and two remotes, then just buying the one remote that was defective.
 

Jim Fairbanks

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Hey nick...here is some more info...Jim..........Notes

STARTING SYSTEM
The PG-260D is a non-repairable starter motor. It has pole pieces that are arranged around the armature. Both solenoid windings are energized. The pull-in winding circuit is completed to the ground through the starter motor. The windings work together magnetically to pull and hold in the plunger. The plunger moves the shift lever. This action causes the starter drive assembly to rotate on the armature shaft spline as it engages with the flywheel ring gear on the engine. Moving at the same time, the plunger also closes the solenoid switch contacts in the starter solenoid. Full battery voltage is applied directly to the starter motor and it cranks the engine.

As soon as the solenoid switch contacts close, current stops flowing thorough the pull-in winding because battery voltage is applied to both ends of the windings. The hold-in winding remains energized; its magnetic field is strong enough to hold the plunger, shift lever, starter drive assembly, and solenoid switch contacts in place to continue cranking the engine. When the engine starts, pinion overrun protects the armature from excessive speed until the switch is opened.

When the ignition switch is released from the START position, the START relay opens and battery voltage is removed from the starter solenoid S terminal. Current flows from the motor contacts through both windings to the ground at the end of the hold-in winding. However, the direction of the current flow through the pull-in winding is now opposite the direction of the current flow when the winding was first energized.

The magnetic fields of the pull-in and hold-in windings now oppose one another. This action of the windings, along with the help of the return spring, causes the starter drive assembly to disengage and the solenoid switch contacts to open simultaneously. As soon as the contacts open, the starter circuit is turned off.

Circuit Description / N~Body 3.4L (LA1)
Moving the ignition switch to the START position sends a 12 V to the PCM Ignition Crank Voltage Sense. At the same time a 12 V signal is sent through the PNP switch then through the coil side of the STARTER relay. The PCM verifies that all parameter a met for starting. The PCM then grounds the control circuit of the START relay. When the START relay is energized it allows voltage to the starter solenoid S terminal.





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