COLD START STALL-FALSE CODE 31,55 & 56 (NEW MEM-CAL)

VEHICLES AFFECTED: 1990 F-CAR WITH 3.1L AND A/T

CONDITION:

Customers may experience cold start stall and/or dealer service may find false Codes 31, 55 and 56 while trying to diagnose the vehicle for various conditions. Also, the VATS system code 46 may not set.

CAUSE:

System component variability plus low fuel volatility.

CORRECTION:

If any of the subject conditions are found, then complete the following procedure:

1. Perform diagnostics, per Section 6E of the Service Manual. Make any adjustments as required, or replace any defective parts.

2. If no other conditions were found using normal diagnostics, and the condition or conditions still exist, then replace the MEM-CAL with one from the following table:

PART NUMBER DESCRIPTION CODE

16150975 MEM-CAL (FED) AUJW

3. (A) Pull the underhood ECM continuous power fuse or disconnect the battery and leave it disconnected for at least 10 min.

(B) Remove current MEM-CAL and install a new service MEM-CAL.

(C) Restore the battery power and place air conditioning controls (if equipped) in the "off" position.

(D) Firmly apply the parking brake and block the drive wheels. Start the engine, and shift the transmission to "drive".

(E) Allow the engine to run until the engine cooling fan has cycled once, or a maximum of 10 minutes.

(F) Turn the ignition key to the "off" position for at least 5 seconds.

(G) Start the engine, and shift the transmission to "drive".

(H) Allow engine to run for at least 5 minutes.

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.