PLEASE help!!!! 2000 STS OBD/computer problems

[David2000sts]

Hello All,

I have a problem:

When the key is turned to on, sometimes the car's lights(dash and exterior and maybe interior) flash off and on for 2 seconds to 30 seconds depending on the occurance. The lights flash very quickly and I can hear 2 switches going on and off - I took out the back seat so I could hear a little better. If the check engine light DOES NOT come on, when I turn the ignition on/start, nothing happens.

sometimes when the ignition is on (not started) the dash will go off and then go through the same cycle as if I turned the key off then on.

If the check engine light does not come on, it says service air bag. Every now and then it says low fuel (it's not)

I went through the codes and have the U1000 (Class 2 Comm malfunction) come up every time after I reset. Sometimes it's the only code, sometimes there is a second or third. P1634 (Ignition 1 switch circuit) has come up a couple times.

After I start, I take it for a spin and there are no codes while I drive and it drives as smooth as ever. Not until I try and start again do codes come up. If the service airbag message comes up, I can't get into the built in OBD. I need to wait until the check engine light is on or the car is running.

I replaced the 2 crank sensors and it didn't fix the problem.

Sometimes I get in the car and it goes right away - other times I turn it off and on for 10 minutes waiting for it.

If it doesn't start, the starter doesn't engage, so it seems like an electronic problem of some sort.

Any help would really be appreciated,

David

[MAC]

I would start by checking the battery cables, especially the positive cable for corrosion at the connection and under insulation. I had a problem with the PCM resetting in my 94 Eldorado because the positive battery cable was corroded. I don't know if my suggestion is applicable to a 2000 STS--Just my 2¢.

[David2000sts]

That was my first thought. I took out the battery, and when I disconnected it, I broke the post and had to replace the battery. When I unbolted the positive terminal, the whole metal part of the battery came off with it. I replaced the battery and checked that all was fine. Thanks, David

[JimD]

Clean / tight battery terminals are a must. Also the battery negative to chassis cable connection at the chassis. And while you are under the back seat, check the fuse labeled IGN SW and the fuse labeled PCM IGN to be sure they are bright and clean.

One more labor intensive step is to inspect and clean the connectors at the PCM (located in front of the engine air filter).

From your description, the Pass-Key module is also a possibility. It would help us if we had the complete list of codes that are set.

[MAC]

Just curious--When the problem occurs do you ever put it in neutral and try to start it?

[David2000sts]

All the fuses were tested and the contacts were cleaned on the battery and at the relay in the back seat. The voltage to the front fuse box is good and so is the voltage to the one in the back seat.

The car still won't start right away. When I turn the key, nothing happens. After I wait a bit, I sometimes hear the fuel pump go, then it will start. Could the modules in the front fuse boxes have anything to do with it? Nothing more embarrasing than driving a nice car that won't start. My mechanic looked at it for 3 hours today and didn't make any real headway.

(I've changed the battery and upper & lower crank shaft sensors)

Any other ideas?

Thanks,

David

[JimD]

Trouble codes; there must be one or more codes set.

http://caddyinfo.com/readingcodes.html

[David2000sts]

Trouble codes; there must be one or more codes set.

http://caddyinfo.com/readingcodes.html

I get the u1000 code every time. Sometimes alone, sometimes with others. I've had about 50 different codes over the last couple weeks - all history, not current.

[JimD]

Trouble codes; there must be one or more codes set.

http://caddyinfo.com/readingcodes.html

I get the u1000 code every time. Sometimes alone, sometimes with others. I've had about 50 different codes over the last couple weeks - all history, not current.

There are several possibilities and one of them is the Pass-Key. Without knowing the codes, you are shooting in the dark. A clue could / should be represented by a "B" code.

The code you are chasing will go to history when the affected system passes the OBD test as indicated by the car starting and running as if nothing is wrong. Run the codes immediately when you have your syptoms.

[David2000sts]

Trouble codes; there must be one or more codes set.

http://caddyinfo.com/readingcodes.html

I get the u1000 code every time. Sometimes alone, sometimes with others. I've had about 50 different codes over the last couple weeks - all history, not current.

There are several possibilities and one of them is the Pass-Key. Without knowing the codes, you are shooting in the dark. A clue could / should be represented by a "B" code.

The code you are chasing will go to history when the affected system passes the OBD test as indicated by the car starting and running as if nothing is wrong. Run the codes immediately when you have your syptoms.

The only consistent code is the U1000. I did take it to the shop where we plugged in the Snap On scanner. The built in code reader won't work when I have the symptoms - I also can't see the information like MPG and Temp. The Air Bag light is also on and it usually says low fuel(it's not).

One thing the mechanic mentioned is that the Snap On tool said there were a lot of bullitens about flashing the PCM.

I'm now leaning towards the Service Air Bag and Low fuel messages being the main symptoms of the problem. Perhaps there is a module or a relay it's attached to?

Thanks

[BodybyFisher]

You should really post all codes, it makes it easier for us to understand potential problems. The Air Bag light if it is on should be posting a current code. Please post all the codes here

[David2000sts]

You should really post all codes, it makes it easier for us to understand potential problems. The Air Bag light if it is on should be posting a current code. Please post all the codes here

No current codes, I've only ever had history codes from the DIC code reader. The codes from the first scan were:

IPC U1000 - Class 2 Communication Malfunction

IRC U1016 - Loss of Communications with PCM

IRC U1129 - Loss of Communications with AMP

PCM P1634 - Ignition 1 Switch Circuit

RIM U1255 - Class 2 Communication Malfunction (Serial Data Line Malfunction)

TTM U1016 - Loss of Communications with PCM

[Cadillac Jim]

You have a network problem. Clear that first, and all your other problems may go away. It's in the wiring between the under-dash computer (instrument panel module) and the PCM.

[JimD]

....

No current codes, I've only ever had history codes from the DIC code reader. The codes from the first scan were:

....

PCM P1634 - Ignition 1 Switch Circuit

....

TTM U1016 - Loss of Communications with PCM

Several things I would do if it was my car.

Try pausing for a heartbeat between ON and START when starting the engine. If you have another key, or the gray colored master key, try using that a few times.

In the underhood fuse box, pull and check / clean / inspect the two fuses identified as PCM IGN and PCM BATT.

If that makes no difference, I would inspect the connectors at the PCM (under and in front of the engine air intake filter). Remove and reinstall the connectors several times to wipe the contacts.

[BodybyFisher]

All GM Vehicles Using Class 2 Communications Diagnostic Strategy for DTC U1000 or U1255 - kw BCM code EBTCM radio RIM #PIT3154 - (Sep 10, 2004)

All GM Vehicles Using Class 2 Communications Diagnostic Strategy For DTC U1000 or U1255

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Condition/Concern:

DTC U1000 or U1255 set current or history, with or without other DTCs

Recommendation/Instructions:

DTC U1000 Class 2 Data Link

DTC U1255 Lost Communications

These DTCs set when the control module does not receive a message that it was expecting from another control module, and does not know which control module did not send that message.

If the DTC U1000 or U1255 is set in history with other DTCs set current or history, diagnose the other DTCs first.

If the DTC U1000 or U1255 set current, this usually indicates a module that is currently not communicating or a configuration issue. For example, if the control module is configured for an option (ie: Onstar, Keyless Entry, Memory Mirrors, etc.) that the vehicle does not have, it may expect to receive a message regarding this missing feature. This would usually occur due to the control module being recently replaced and incorrectly setup.

When the DTC U1000 or U1255 is current, the module that is not communicating may not even be listed on the Tech 2 on the Diagnostic Circuit Check/Class 2 Message Monitor list.

If the DTC U1000 or U1255 has set in history without other DTCs, replacing the control module setting the DTC is most likely NOT the solution. The module that has set the code is looking for an input from another module that is not communicating. Since the module did not receive an input that it is expecting to see, it sets a U1000 or U1255 which indicates there was a loss of communications. Look at the customer’s complaint (ie: intermittent, erratic tachometer operation); this will probably be a better indication of the control module that is the source of the concern.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

Models:

(All GM vehicles using Class 2 communications)

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DTC U1000 and DTC U1255 Class 2 Communication Malfunction

Refer to one of the following Data Link Connector (DLC) Schematics:

Data Link Connector Power and Ground (LH Drive)

Data Link Connector Power and Ground (RH Drive)

Circuit Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring (Node Alive messages). A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least one critical parameter within about five seconds of beginning serial data communication, DTC U1000 or U1255 DTC is set. When more than one critical parameter does not have an identification number associated with it, the DTC will only be reported once.

Conditions for Running the DTC

Diagnostic trouble codes B1327, U1300, U1301, and U1305 do not have a current status. Any particular device on the class 2 serial data circuit will support some subset of these DTCs.

The vehicle power mode (ignition switch position) requires serial data communication to occur.

Conditions for Setting the DTC

At least one critical operating parameter has not been associated with an identification number within about five seconds after beginning serial data communication.

Action Taken When the DTC Sets

The module uses a default value for the missing parameter.

Conditions for Clearing the MIL/DTC

A current U1000 or U1255 DTC will clear when all critical operating parameters for the module have been associated with an identification number or at the end of the current ignition cycle.

A history U1000 or U1255 DTC will clear upon receipt of a scan tool Clear DTCs command.

Diagnostic Aids

When a malfunction (such as a blown fuse to a module) occurs while modules are communicating, a Loss of XXX Communication DTC is set current. When the modules stop communicating (ignition is turned off) the current Loss of XXX Communication DTC is cleared but the history DTC remains. When the modules begin to communicate again, the module with the blown fuse will not be learned by the other modules so a U1000 or U1255 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only a U1000 or U1255 is set.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

A Loss of (Specific Module) Communication DTC (U1001 - U1199) with a history status may indicate the cause of U1000 or U1255.

The module(s) not communicating is the likely cause of a U1000 or U1255 DTC. The modules available are listed under Class 2 Serial Data Link. Refer to Data Link Communications Circuit Description .

The module which was not communicating due to a poor connection to the class 2 serial data circuit may have set Loss of (Specific Module) Communication DTCs (U1001 - U1199) for those modules that it was monitoring.

The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.

If all modules are communicating, the module which set U1000 or U1255 DTC may have done so due to some other condition.

The module which set the U1000 or U1255 is the likely cause of the malfunction.

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Data Link Communications Circuit Description

Data Link Connector (DLC)

The DLC is a standardized 16 way connector located below the instrument panel and close to the steering column. Both the connector design and location are dictated by industry wide agreements.

All DLCs are required to provide a power supply, hot at all times, to Pin 16. This circuit is used to power the scan tool. All DLCs supply a power ground at Pin 4 and a clean signal ground at Pin 5.

The Class 2 serial data circuit is provided at Pin 2 of the DLC.

The Class 2 Serial Data Line CKT 1807 (PPL) is wired to the DLC at terminal 2.

Class 2 Serial Data Link

The data link is configured as a ring with discrete lines entering and leaving each module. This allows communications to the modules on the ring if one of the two discrete circuits is open.

The control modules on the Class 2 Serial Data Line can include the following:

Cellular Telephone Module

Continuously Variable Road Sensing Suspension (CVRSS) Module

Dash Integration Module (DIM)

Driver Door Module (DDM)

Electronic Brake Control Module (EBCM)

Inflatable Restraint Sensing and Diagnostic Module (SDM)

Instrument Cluster (IPC)

Instrument Panel Integration Module (IPM)

Memory Seat Module (MSM)

Navigation Data Processor

Powertrain Control Module (PCM)

Radio

Radio Amplifier

Remote Keyless Entry (RKE) Module

Rear Integration Module (RIM)

Steering Column Module

Theft Deterrent Module

Simple Bus Interface (SBI) Serial Data Line

SBI does not communicate with the scan tool via the DLC. SBI information is interpreted by the driver door module (DDM) and transmitted on the Class 2 data link by the DDM.

The simple bus interface (SBI) is used for serial data communication between the four door modules as well as the driver door switch (DDS).

Refer to Diagnostic System Check - Power Door Systems