EXPERTEC TSB (91-6E-36)

WARNING: This page is about the Forward Control 3.9 L, NV4500/MT8, which is a different variant/trim than selected.

Publication date: 1990-11-14
Reference number: 91-6E-36

EXPERTEC TSB

TECHNICAL SERVICE BULLETIN

Reference Number(s): 91-6E-36, Date of Issue: 11/14/90

INTERMITTENT CONNECTION AT ECM - PCM/TCM SENSORS OR COMPONENTS

Model(s): 1991 GMC Light and Medium Duty Truck Models with ECM/PCM/TCM

Bulletin No.: GMC 91-6E-36

Date: 11/14/1990

BULLETIN ILLUSTRATION LIST

Fig 1: Graphic

SERVICE INFORMATION

Some 1991 Light and Medium duty trucks equipped with Electronic Control Modules (ECM) or Powertrain Control Modules (PCM) or Transmission Control Modules (TCM) may experience a condition in which the female terminals (150 series Metri-pack) in certain sensor or component connectors do not make a solid connection to the male terminals in the opposing connectors. This can result in a intermittent connection. The 1991 Driveability & Emissions Manual (X-9136) directs a check of connections anytime an intermittent condition is found.

The following chart lists the component and circuit numbers that may experience this condition.

AFFECTED COMPONENT AND CIRCUIT NUMBERS

Component	Circuit	Description
Intake Air Temperature	472	IAT signal
(IAT) 2.5L only	469	5 volt return (ground)
Coolant Temperature Sensor	410	CTS signal
(CTS)	452	5 volt return(ground)
Throttle Position Sensor	417	TPS signal
(TPS)	452	5 volt return (ground)
Electronic Spark Timing Module	453	EST Reference low
(EST)	424 430 423	EST Bypass EST Reference high EST Control
Transmission Vehicle Speed Sensor	821	Speed Signal high
(All Auto. & Manual Transmission)	822	Speed Signal low
Transmission Input Speed Sensor	1230	Input Speed Signal low
(4L80E only)	1231	Input Speed Signal high
Transmission Output Speed Sensor	1232	Output Speed Sensor high
(4L80E with Four Wheel Drive only)	1233	Output Speed Sensor low

If an intermittent condition is found, the following test procedure should be performed.

Insert a new mating male terminal, P/N 12047581 or 12045773, into the female terminal and check for a slight drag when the terminals are separated. Loose terminals without drag should be replaced. If the amount of drag is questionable, remove the terminal from the connector and inspect the terminal for the condition shown in FIGURE 1. Replace any terminals found defective with terminal P/N 12047680.

General directions of terminal replacement can be found on pages 3-146 thru 3-147 of the 1991 Driveability and Emissions Manual.

NOTE: Do not attempt to repair a defective terminal. All of the above terminal part numbers are contained in J-38125 or are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

Labor Operation: T7096

Labor Time: This is a ST (Straight Time) operation which requires time documentation as detailed in the claims processing manual. Zone approval is required beyond .5 hours.

NOTE: Labor Operation is coded to base vehicle coverage in the warranty system.