CPS circuit

I am having trouble with the dashboard odometer and other displays that come on when door handle is pulled. Powers up as normal. When shut off with key RAP works normally, as soon as door opened RAP turns off then about 20 seconds later odometer and door handle lights and shift position imdicater come back on and stay on. Pulling the CPS fuse shuts everything off. For some reason my computer will start the download of FSM then stays there until I shut off computer. When I tried to use this stupid tablet it comes back, download unsuccessful. Any ideas. What does the CPS fuse do, where does it get its power from. Ever since I bought this car the items controlled by the body computer sometimes go wonky, courtesy lights intermittent etc. I have a feeling it finally failed. All ideas gratefully accepted.

Thank you all,

Richard.

Central power supply provides the filtered supply voltage and "wake up" signal to the major modules in the cars network. I would suspect BCM problem causing the displays to stay "up" before the CPS. The BCM reads the switch inputs and controls the lighting and display outputs so a failure there could account for the this and the courtesy light problems you've noted.

Pulling the CPS fuse is probably shutting things off indirectly as it is forcing the BCM to power down, thereby taking the displays with it.

Also some chance it could be an ignition switch problem putting the car in run or accessory mode after shut down. That would also cause the IPC to come back online. Is the CRT active while this is happening as well? If so, what is it showing; the Reatta logo, summary screen or radio screen? Also, is it doing the full light show after the 20 second delay or is it coming up like the car is running?

I'd start with the simple stuff first. Go into diagnostics and verify proper function of the door handle and jamb switches by cycling each on both doors while monitoring the respective BCM inputs. After ruling those out, we can move on to other possible culprits.

KDirk

Thanks KDirk, accessories are not operable when switch is in off position even when ipc is on. After turning key to off accessories, radio, windows, etc work until door is opened so I believe the rap is working properly. I am going to use a friend's computer and find the proper diagram, then i can enter diagnostic mode. I have a feeling it is the bcm, my 90 doesn't have the crt, but the odometer comes on as if you jut opened the door. Before if you didn't start the car it would fade out in around 20 seconds, now it stays on.

Thank you for your time,

Richard.

Oops, didn't realize you had a 90. The odometer only display is the 1990 equivalent of the light show. It is normally activated on entry and stays on for about 20 seconds. Sounds very much like an internal BCM failure to me especially if you are getting the full IPC display while the car is off. Is the climate control panel also on when this happens?

KDirk

KDirk, I don't get the full ipc display unless key is in on position. I get the odometer, backlight on A/C controls and the little lights in the door above the door open handle. I just went to check the charger and it had gone to trickle mode. Disconnected the charger and put the CPS fuse in place. Everything stayed dark. Started engine and ipc was fine. Shut off engine and waited for a few minutes and odometer did not come on, everything working as it should. Started to rain so I pulled the cps fuse to save the battery if system failed again, I will replace the fuse later today and check on it every hour or so. Don't you love intermittent problems?

Thanks for your help,

Richard.

They really can test your resolve and patience.

Suggest you do the door handle switch test as KDirk recommended as one of these could go out of kilter and keep telling BCM to turn courtesy lights on and display odometer reading.

It is step 5 of this procedure on Ronnie's site:

http://reattaowner.com/roj/component/content/article/59-lighting-system/interior-lights/193-door-switch-troubleshooting-guide

Do it on both doors. If you haven't done so before, clean the ground terminals under the hood per this procedure:

http://reattaowner.com/roj/component/content/article/62-electrical-system/other-electrical/224-ground-terminals-junction-box-location

A bad ground or poor power connection can create lots of mysterious gremlins in these cars. If problem recurs, disconnect connectors on BCM and reconnect. Hopefully a BCM replacement won't be needed.

Thanks Mc Reatta, I don't have access to a computer that will let me go to reatta.net right now. Can someone please tell me where the micro relay center, position B is? There is a block im the right side of the trunk that has 4 relays, is that it? Which one is position B.

MANY THANKS!

I THINK I WILL GIVE UP! When I check the bcm inputs the testfor the door handle will go from hi to low when lifting the handle then goes back to hi. On the output tests B004 courtesy lamp relay it displays hi then lo about once a second with no input changes and I can hear a relay click as it changes. Same thing on B003 rap relay, however the rap is working fine. I think this means the bcm has failed. Any ideas on cost for a replacement? I am going to drive the Skylark for a while, but that means I will have to keep it outside which will be bad for the forty three year old factory paint. HELP!

Thank you all,

Richard

I THINK I WILL GIVE UP! When I check the bcm inputs the testfor the door handle will go from hi to low when lifting the handle then goes back to hi. On the output tests B004 courtesy lamp relay it displays hi then lo about once a second with no input changes and I can hear a relay click as it changes. Same thing on B003 rap relay, however the rap is working fine. I think this means the bcm has failed. Any ideas on cost for a replacement? I am going to drive the Skylark for a while, but that means I will have to keep it outside which will be bad for the forty three year old factory paint. HELP!

Thank you all,

Richard

You asked about relay B in your previous post. Remove the door on the console on the passenger side. This is what you should see.

The back of your door should tell you what each relay does.

I am having trouble with the dashboard odometer and other displays that come on when door handle is pulled. Powers up as normal. When shut off with key RAP works normally, as soon as door opened RAP turns off then about 20 seconds later odometer and door handle lights and shift position imdicater come back on and stay on.

Thank you Ronnie, I found those relays, I think it is the courtesy light relay, however the courtesy don't blink or work at all for that matter. When I ground the dome light terminal all the lights come on, I might have a bad ground for the lighting circuit, when I can get back on a real computer I will look at the FSM.

Best Regards,

Richard.

Yes, when I did the bcm input tests all showed good.

That's what the output tests are supposed to do. They cycle a circuit on and off so you can verify the operation of the relay, solenoid etc.

If anything, that makes me think the BCM is OK since it can control the courtesy light relay.

The courtesy lights should have gone on and off as BO04 cycled. Did they?

Might want to broaden the list of inputs to check to all of them that will turn the courtesy lights on.

Add BI01 and BI05 to your BI06 Input tests. BI05 and 06 have to be done for both doors. If they are all HI and go LO when switch is operated, then nothing is telling the BCM to turn the courtesy lights on.

Believe when the key is turned to run, the BCM will display the odometer reading, but not turn on the courtesy lights. The RKE piggybacks on the handle switch circuit BI06 so if the door switches respond that should be OK too.

If they all are OK, there's not much left but the BCM.

Thank you Ronnie, I found those relays, I think it is the courtesy light relay, however the courtesy don't blink or work at all for that matter. When I ground the dome light terminal all the lights come on, I might have a bad ground for the lighting circuit, when I can get back on a real computer I will look at the FSM.

Best Regards,

Richard.

Thanks Mc Reatta, I did check the inputs to the bcm and all are good. It would seem that since I no longer have any courtesy lights and in the past they were intermittent sometimes dimming then coming back to full brightness and the fact that when I ground the dome light terminal and they come on makes me think I have two problems, bad ground in courtesy light circuit and a failing bcm that sends a turn on signal no matter if the handle is lifted or not for the odometer and climate control panel and interior door handle. The joy of trying to keep a 25 year old orphan car for a daily driver. I really can't complain, in 5 years I may have spent $500.00 for repairs, including new ac compressor with the needed parts to go with it and that 500 dollars includes my mechanics labor. I was very lucky to find him. He is honest and if the repair takes more hours than he quoted he will not charge for the extra time. Small 3 man, 2 lift shop 5 blocks away.

I have to agree there is more than one thing going on here.

The courtesy lights are on a different circuit than the ECU, radio, and door handle cup lights.

You will find your courtesy light problem either at the splice under the passenger's seat, the relay in the trunk, or the ground post on the rear shelf near the third brake light. First step wound be to swap the CL relay in the panel on the right side of the trunk with an adjacent one and see if the lights start working. Then check the ground post is clean and tight. Otherwise it's pull the seat out and check the splice in the blue and white wires.

The ECU and door handle cup "flood lights" etc. are run off the dimming circuit. They should only come on when the twilight photocell tells the BCM it's dark out and the ignition is in run. Then the BCM tells the IPC via the data lines to turn on those lights in accordance with the dimmer slider input. Powering up the BCM will also tell the IPC to display the odometer reading via those data lines.

So there are many more things to look at now. Do those lights come on when the key is in the off position or only with the key in run? Is the car in the dark, or do they come on in the sunlight when they are on? Do you have a 90 headlight switch installed, or a 91 / Riviera type switch with twilight sentential in lieu of the fog light switch?

I have the stock headlight switch, the handle floodlights and odometer and climate control backlight will come on as if someone pulled the outside door handles with no one touching the car, after turning key to on or starting engine when turned off the odometer, climate control backlight and handle floodlights turn off for about 20 to 30 seconds then come back on. When BCM input tests B101 to B106 show proper response. B106 is the door handle input. I also checked the BCM data for the dimming pot at BD42 and it gave correct readings, as I scanned from BD20 all readings were in spec.

Thanks for your help on the ground locations for the courtesy lights, in the past sometimes they would flicker then go to full brightness, I will hunt that one down after I figure out the BCM gremlin. I am thinking it is the BCM itself because it is showing the proper inputs, do you agree?

Best regards,

Richard.

You should not get those lights on unless the key is in run and the twilight photocell is over 70 (if I remember correctly). So there is either a problem with the ignition switch, or the BCM is bad thinking the car is in run when it isn't. If the IPC responds correctly to the ignition key (dark when off, lit in run) then it's almost surely the BCM is bad.

If you swap in another, move both EPROMs to the replacement BCM to maintain the correct program, and the correct VIN and odometer data.

This should correct the odometer and door flood light issue, but I believe the courtesy light issue will remain until you find out what's keeping them from reaching the ground post in the trunk.

Mc Reatta I agree with you and once again I want to thank all the folks that makes this the best car forum on the net. Ronnie says the Reatta store has BCMs in stock new! Gm must have used this module in a bunch of cars for a new one to be available.

BEST REGARDS TO ALL,

Richard

Mc Reatta I agree with you and once again I want to thank all the folks that makes this the best car forum on the net. Ronnie says the Reatta store has BCMs in stock new! Gm must have used this module in a bunch of cars for a new one to be available.

BEST REGARDS TO ALL,

Richard

Sorry Ronnie, my mistake. I just missed that part. I could blame the screen on this tablet but im reality my eyes missed it. I'm sure the rebuilt will be fine.

Richard