Description of Data Line Conditions

This section explains how to find the cause of a data line condition that is present all the time or can be duplicated for diagnosis. Using the instructions in this section, perform the appropriate "condition present diagnosis" trouble tree.

The condition present diagnosis charts have many branches that instruct to check for voltage/ground on the 800 circuit. First, check for voltage at the specified pin with the ignition on (there should be less than .1 volts). If there is no voltage, check the circuit for resistance to ground (should read open to ground on the highest resistance setting). The trouble trees are written so that whenever these checks are made the right components are connected/disconnected to prevent false readings. Therefore, do not reconnect components until instructed to do so or when diagnosis is completed.

If the voltage/resistance test indicates there is a problem in part of the 800 circuit, check that section of the 800 circuit by tracing the wire and checking connections in that segment. Refer to page 8A-50-0 in the Chassis Service Manual for circuit layout. If the circuit is difficult to trace or no problem in the circuit is visible, it may be better to restring the segment involved.

Note:
Data line conditions tend to be intermittent and may disappear while disconnecting/reconnecting components. Therefore, double check each step of the trouble tree to make sure the conditions have not disappeared during testing. If they have disappeared, return to the last step taken while the condition was present and continue when condition returns. If the condition cannot be duplicated again or the condition present diagnosis does not lead to the fix, perform the condition not present diagnosis.

CONDITION NOT PRESENT:
Sometimes the conditions can be duplicated by carefully warming the data line components with a heat gun and/or lightly tapping on them. If the condition cannot be duplicated on the vehicle during diagnosis, follow the procedure below:

1. Make sure that the grounds on the block near the starter solenoid or behind the power steering pump behind the engine block and on the fender near the battery, are clean and tight. Make certain there are star washers on the stud and that the studs are free of corrosion.

2. Check the BCM EPROM and EEPROM and ECM PROM or MEM-CAL assembly for proper insertion into their respective sockets. Inspect components for bent or damaged legs.

3. Make sure both BCM and ECM have the correct PROM's for that model year.

4. If the source of the intermittent problem has not been found and the intermittent condition persists:

A. Verify good connections at the following components. Check each connection for proper latching and pins seated in the connector.

B. Remove the following components, one at a time, in the order shown, using the Toronado/Trofeo Service Manual Section 8A-50. Jumper the 800 circuit while checking for reoccurrence of the intermittent condition. The order listed represents most likely to least likely cause of a multiple communications code condition:

Oldsmobile:

^ ECC Head
^ BCM
^ Programmer
^ ECM
^ Central Power Supply (CPS) (on 1986-90 models)
^ BCM EPROM
^ IPC
^ Chime Module (on 1986 and 1987 models only)
^ ECM and EPROM
^ BCM EEPROM