Gauge Control Module (Tach) Input Test

Gauge Control Module (Tach)


1.Turn the ignition switch OFF.

2.Remove the gauge control module (tach).

3.Disconnect the gauge control module (tach) 36P connector.

 

4.Inspect the connector and socket terminals to be sure they are all making good contact.

  • If the terminals are bent, loose or corroded, repair them as necessary, and recheck the system.
  • If the terminals are OK, go to 5.

5.With the connector still disconnected, make these input tests at the connector.

  • If any test indicates a problem, find and correct the cause, then recheck the system.
  • If the input tests prove OK, go to 6.

Cavity Wire Test condition Test: Desired result Possible cause if result is not obtained 
18 WHT Under all conditions Check for voltage to
ground:
There should be battery voltage. 
  • Blown No. 16 (15 A) fuse in the under-hood fuse/relay box
  • An open in the wire
 
17 LT BLU Ignition switch ON (II) Check for voltage to
ground:
There should be battery voltage. 
  • Blown No. 10 (7.5 A) fuse in the under-dash fuse/relay box
  • An open in the wire
 
20 LT GRN Under all conditions (disconnect the gauge control module (speedo) 12P connector) Check for continuity between the No. 20 terminal and gauge control module (speedo) 12P connector No. 7 terminal:
There should be continuity. 		An open in the wire 
Attach to ground:
There should be no continuity. 		A short to ground in the wire 
13 BLU Combination light switch ON Attach to ground:
The dash lights (LED) come on. 
  • Dash lights (LED)
  • An open in the wire
 
14 PUR Combination light switch ON Attach to ground:
The dash lights (BULB) and audio unit light come on. 
  • Faulty dash lights (BULB)
  • Faulty audio unit light
  • An open in the wire
 


6.Reconnect the connector to the gauge control module (tach), and make these input tests at the connector.

  • If any test indicates a problem, find and correct the cause, then recheck the system.
  • If all the input tests prove OK, the gauge control module (tach) must be faulty; replace it.

Cavity Wire Test condition Test: Desired result Possible cause if result is not obtained 
15 BLK Under all conditions Check for voltage to ground:
There should be less than 1 V. 
  • Poor ground (G502)
  • An open in the wire
 
16 BLK Under all conditions Check for voltage to ground:
There should be less than 1 V. 
  • Poor ground (G503)
  • An open in the wire
 

Cavity Wire Test condition Test: Desired result Possible cause if result is not obtained 
24 LT BLU Ignition switch ON (II), select/reset switch pressed Check for voltage to ground:
There should be less than 1 V. 
  • Poor ground (G503)
  • Faulty select/reset switch
  • An open in the wire
 
Ignition switch ON (II), select/reset switch released Check for voltage to ground:
There should be 5 V or more. 
  • Faulty select/reset switch
  • A short to ground in the wire
 
25 GRN Ignition switch ON (II), information switch pressed Check for voltage to ground:
There should be less than 1 V. 
  • Poor ground (G503)
  • Faulty information switch
  • An open in the wire
 
Ignition switch ON (II), information switch released Check for voltage to ground:
There should be 5 V or more. 
  • Faulty information switch
  • A short to ground in the wire
 
27 ORN Ignition switch ON (II), brake fluid is full level in the reservoir Check for voltage to ground:
There should be less than 1 V. 
  • Poor ground (G401)
  • Faulty brake fluid level switch
  • An open in the wire
 
Ignition switch ON (II), brake fluid is lower level in the reservoir Check for voltage to ground:
There should be 5 V or more. 
  • Faulty brake fluid level switch
  • A short to ground in the wire
 
28 LT GRN Ignition switch ON (II), parking brake lever pulled Check for voltage to ground:
There should be less than 1 V. 
  • Faulty parking brake switch
  • An open in the wire
 
Ignition switch ON (II), parking brake lever released Check for voltage to ground:
There should be 5 V or more. 
  • Faulty parking brake switch
  • A short to ground in the wire