GMC 1976 ZEO 6083 Maintenance Manual page 646

CRUISE CONTROL SYSTEM DIAGNOSIS
CHASSIS ELECTRICAL 12- 41
PROBLEM CAUSE
CORRECTION
Will Not Engage - System Brake switch circuit open .
Check connections - adjust or replace the
Inoperative
Clutch switch circuit open .
switch . Refer to Electrical Check Out .
Fuse blown .
Replace fuse - if it blows again, check for :
1 . Engage switch stuck in the center of
travel - Refer to Electrical Check Out .
2 . Incorrect wiring - Refer to Electrical
Check Out .
3 . Short to ground - Refer to Electrical
Check Out .
Make necessary corrections .
Defective Engage switch .
Replace as needed - Refer to Electrical
Check Out .
Vacuum leak in Servo and/or Brake switch Vacuum test and repair or replace as need-
and connecting lines . Vacuum hose notcon-
ed . Refer to Servo and Vacuum System
nected to vacuum switch .
Check Out .
Vacuum Release switch misadjusted Readjust switch .
(always open) .
Crossed hoses at transducer .
Reroute hoses .
Open in wiring harness .
Repair or replace as needed .
Pinched or plugged hose that is connected
Free or replace hose .
to the Servo .
Defective transducer .
Replace transducer .
Chain from Servo to carburetor discon- Connect chain .
nected .
Does Not Cruise at Engagement Orifice tube misadjusted .
Adjust as required .
Speed
System Hunts, Pulses or Surges
Kinked or deteriorated hoses (air leak) . Repair or replace .
Defective and/or improperly positioned
Repair or replace as needed .
drive cables and or casing assemblies .
Defective transducer .
Replace transducer .
System Does Not Disengage -
Brake and/or Vacuum switch misadjusted
Adjust or replace as required . Refer to
With Brake Pedal or defective .
Servo and Vacuum System Check Out and
Electrical Check Out .
Wires which should be connected to the
Reroute wires to stop light switch .
pedal switch(es) connected tothefuseblock .
System Steadily accelerates or Manifold vacuum connected directly to Servo . Reroute hose .
Applies Full Throttle When
Engaged
Defective transducer .
Replace transducer .
Cannot Adjust Speed Downward
Defective Engagement switch or wiring .
Replace as needed . Refer to Electrical
With Engage Button
Check Out .
Does Not Engage or Engages Defective transducer .
Replace transducer .
Lower Than Limits Referred
To In "Driver Operation ."
Low Speed Engagement Can
BE as Low As 20 MPH .
Slow Throttle Return to Idle Pinched air hose at vacuum release switch .
Free or replace hose .
After Brake is Depressed
System Operates Correctly, But
Crossed vacuum hoses at transducer . Reroute hoses .
Constant Vacuum Bleed When
System is Disengaged
High Engine Idle Speed - Inde- Tight Servo chain .
Loosen adjustment .
pendent of Carburetor Adjust-
ments . Constant Air Bleed
Through Systen .
Constant Drain on Battery Power lead connected to "Fused Battery"
Reroute to "Fused Ignition" terminal .
terminal of fuse block .
System Can Be Engaged At Idle
Wires reversed at transducer .
Reverse wires .
By Depressing Switch, But Will
Drop Out When Switch Is Re-
leased . Solenoid Can Be Heard
When Switch Is Depressed
When Vehicle Is Standing Still