SERVICE MANUAL UPDATE-SEC.7A2 A/T CONTROL MODULE DIAGNOSIS

Subject: AUTOMATIC TRANSAXLE CONTROL MODULE DIAGNOSIS

Model and Year: 1990 PRIZM

The following information should be used in addition to the diagnostic information already in A240E Automatic Transaxle General information and On-Vehicle Service Section 7A- 2 of the 1990 GEO Prizm Service Manual Supplement. (ST 373-90 Supp.)

AUTOMATIC TRANSAXLE CONTROL MODULE DIAGNOSIS Figures 1 through 4

For Automatic Transaxle Control Module system diagnosis, see Automatic Transaxle Diagnostic Charts (Figures 1 through 4).

The diagnostic code is indicated by the number of times the "O/D OFF" lamp flashes (Figure 7).

- If the system is operating correctly the lamp will flash continuously every 0.25 seconds (Figure 8).

- In the event of a malfunction, the lamp will flash every 0.5 seconds. The number of flashes will equal the first digit of the two digit diagnostic code. After a 1.5 second pause, the second set of flashes will equal the second digit of the two digit diagnostic code. There will be a 4.5 second pause before the code repeats itself. If there is more than one code stored in the automatictransaxle Control Module the smaller number of codes will appear first and continue to the larger (Figure 9 and 10). (The pause between two different codes will be only 2.5 seconds.)

1. After the malfunction has been corrected the code(s ) will still be stored in the Automatic Transaxle Control Module. To clear the codes, remove the Dome Fuse from Junction Block 2 for at least 10 seconds with the ignition switch "OFF" (Figure 11) (The ambient temperature affects the amount of time it takes to clear the codes; the lower the temperature the longer the time necessary to clear the codes.)

Important

* Codes can also be cleared by removing the battery negative (-) terminal for at least 10 seconds, but other memory systems (clock, radio, etc.) will also be cleared.

* Codes can be cleared by disconnecting the Automatic Transaxle Control Module connector for at least 10 seconds.

* If the diagnostic code is not cleared, it will be retained by the Automatic Transaxle Control Module and appear along with a new code in the event of a future malfunction.

2. After clearing all codes, road test the vehicle to confirm that a "normal code" is now read on the "O/D OFF" indicator lamp.

Refer to Figure 12 for voltage readings at Automatic Transaxle Control Module connector cavities.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.