1990 reatta won't go into diagnostics mode.

[Guest spiering.lucas]

Alright problem started a couple weeks ago. Check engine and service a/c lights are on. When you hold the off and temp up button on the hvac center the car flashes all the lights on the dash real quick as if it is about to enter diagnostic mode and then nothing happens. Other symptoms include the following. Odometer trip counter will not reset. When you reset the trip meter the trip reads zero and will remain at zero even of the vehicle is driven. After the car has been shut off and turned back on the trip meter returns to normal function and the miles you have put on the car in the mean time have een added to your total. Not the odometer still works when the trip meter us stuck on zero. The last symptom is yesterday on my way home from work the whole dash went black and read 00 and error. I got home turned the car off turned the car back on and everything returned to normal working condition. I have checked all of my fuses and they are all good. I have tried disconnecting my batter. This reset the trip meter and the service ac and check engine light. Shortly after the dash lights service engine and ac came on again. I tried unplugging all the ECM and Power fuses and then putting them back in. This reset the trip meter but the trouble codes remained but I was then able to enter the diagnostics mode. I reset my b codes and e codes and drove the car a couple days. The same dash lights appeared again a few days later and tried to enter diagnostics mode and again nothing. The lights all light up as if it were going to enter DM and then nothing. And that's where I leave off. Any help would-be greatly appreciated.

[KDirk]

What B codes did you have when you cleared them? This combination of symptoms sounds like a probable BCM problem, but could possibly be an IPC malfunction. If the latter, it's not a failure mode that I have seen before.

KDirk

[Guest spiering.lucas]

Well don't remember what the codes were and now I can't get the car to go back in DM so I can't currently provide you with that information. However the last I recall the b codes were for the a/c

[padgett]

On a 90/91 my experience is usually the OFF button not working. Do both work individually ?

On the whole it sounds like your system may have some wires crossed. Keep in mind that you should be able to read ECM codes by jumpering A-B on the ALDL and counting the SES light flashes just like an ordinary GM car.

[Guest Mc_Reatta]

Was another forum member complaining of this problem a while ago. If I remember properly, that case turned out to be a bad BCM.

You should inspect the common power and ground points under the hood behind the battery to make sure they are both clean and tight. Could be a bad connection, but am leaning toward a bad BCM.

I'll try to find that other thread and create a link.

[Guest spiering.lucas]

Thanks

[Guest spiering.lucas]

Yes all the buttons work indiv. Off works

[Guest Mc_Reatta]

Similar thread links:

http://forums.aaca.org/f116/cannot-enter-diagnostic-mode-270810.html

http://forums.aaca.org/f116/no-restart-after-warm-up-298782.html

http://forums.aaca.org/f116/help-abs-warning-light-problem-223763.html

In all of these threads there is a mention of not being able to enter diagnostics mode. Unfortunately, there is no answer to why they won't. Some think it's an IPC problem, some a BCM problem after the control pad for the ECC has been cleaned and determined to be working correctly.

The issue with the trip odometer only and not the odometer and the dash going blank is making me lean towards the IPC more than the BCM.

Wish there was a hard answer posted as to what the problem was for these folks.

[padgett]

Trip odo is stored in ram, resets if you lose keep-alive power to the BCM, main odo is in EEPROM & survives power loss. BCM also drives IPC but "test lights" button should still work without BCM.

[KDirk]

Yep,

Add to that that since all other IPC displays seem to be normal (no mention was made of other problems like loss of gauges except for the brief 00/error display) I suspect a failed/failing BCM. The combination of symptoms listed in the OP is rather odd, and not really typical of a bad IPC. If the IPC is loosing trip odo data, it should be losing all data, resulting in no displays (00/error) and "electrical problem" telltale.

The fact that it tries (and aborts) entry into diagnostics, evidenced by the brief flash of the IPC all segment test seems to indicate that the BCM is backing out of service mode before it gets there. Remember, the BCM is the bus-master for the entire network in the E platform cars. While it was recently shown that the car will run with only an ECM present, the BCM coordinates all other non-powertrain functions and controls the flow of data around the network. If it goes south, all manner of strangeness - up to and including complete failure of the network - can occur.

KDirk

[Guest wally888]

I had the set to zero and won't go in to diagnostics problem on a previously owned car. Both problems were interrmittant. Same symptoms as your but patience (trying to enter diagnostics often) paid off.

[Autry]

On 7/10/2011 at 9:52 PM, padgett said:

On a 90/91 my experience is usually the OFF button not working. Do both work individually ?

On the whole it sounds like your system may have some wires crossed. Keep in mind that you should be able to read ECM codes by jumpering A-B on the ALDL and counting the SES light flashes just like an ordinary GM car.

 

[Autry]

You're right with the paper clip diagnostic but my 1991buick riviera wont go into diagnostic mode anymore and wont crank sometimes and runs crappy and stalls. The service soon light been on for years and ran fine and would allow me to use the diagnostic mode but now the service soon light disappeared the paper clip trick doesn't work anymore I don't know what to do 

[EmTee]

This sounds like an ECM problem - but before replacing the ECM, try disconnecting, cleaning and reconnecting it.  Another possibility is a poor ground connection.  If you have a wiring diagram, check resistance to ground with an Ohm meter between each ground pin on the ECM connectors and the negative battery post.

[2seater]

I know the 91 is different relating to the ECM/BCM being more integrated but are all the functions now in a single silver box?