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Old 07-03-2012, 01:24 PM
justinlogue5_0 justinlogue5_0 is offline
Learning to use the forums
Join Date: Apr 2012
Posts: 11
Default Re: Cruise control problems

I know this is an old thread but I found this and it really helped me so I thought I would share incase some one else needs it.

To test, use a 12 volt testlight and check the 10 amp fuse, #6, in the interior fuse box. If blown, replace and recheck operation. If the fuse is OK, gain access to the Speed Control Amplifier (AMP) behind glove box opening and check for power at pin 4, Dark Blue/Light Green wire, of the small connector. If no power, repair the open between fuse and AMP. If OK, check the grounds at the Pink/Orange and Black wires of the small connector and repair as needed. If OK, go to step 3.

To test, verify the Stop Lamp operation with the brake pedal applied. If there are no Stop Lamps, check for voltage to the Stop Lamp Switch on the Light Green/Red wire. If no voltage, test and replace the 15 amp stop lamp fuse in the interior fuse box or repair the open circuit as needed and recheck the system operation. If OK, check for voltage out of the Stop Lamp Switch on the Light Green wire with the brakes applied. If no voltage, replace the Stop Lamp Switch and retest. If OK, test the Light Green wire at Pin 6 of the small connector at the Speed Control Amplifier (AMP) with the brakes applied. If no voltage is present, repair the open in the circuit from the Stop Lamp Switch to AMP. If OK, go to step 4.

To test, verify proper speedometer operation. If inoperative, refer to available resources for speedometer diagnostics. If OK, backprobe pin 3, Grey/Black wire, at the small connector at the Speed Control Amplifier (AMP) with a digital voltmeter set on AC volts. Raise the rear of the vehicle and monitor AC volts as the vehicle is accelerated to 30 and 45 MPH. Typical AC volts at 30 MPH would be greater than 2.5 volts with a minimum spec of 1.4 volts. At 45 MPH, expect to see at least 3.2 volts with a minimum spec of 1.6. If no or low voltage, replace the Vehicle Speed Sensor (VSS) and recheck operation. If OK, go to step 5.

NOTE: all values may vary plus or minus 0.5 volts. To test, use a digital voltmeter and backprobe pin 5, Light Blue/Black wire, in the small connector at the Speed Control Amplifier (AMP). With the key on and no switches depressed, check for a reference voltage of about 7.8 volts. Next depress and hold the On button. Voltage should read about battery voltage. Depressing the Coast button should read 1.7 volts, Set/Accel should read 4.5 volts, Resume should read 6.3 volts and Off should drop to 0.0 volts. If any readings vary greatly, replace the Speed Control Switches and retest. If OK, go to step 6.

To test, with engine at idle backprobe the White/Pink and Grey/Black wires in the large connector at the Speed Control Amplifier (AMP) and check for battery voltage. If no battery voltage is present, unhook the connector and check the servo circuit continuity. Start with 1 lead on the Orange/Yellow wire and the other on the White/Pink wire. This reading should be between 60-190 Ohms. The next reading would be Orange/Yellow wire to Grey/Black wire. This should read 40-125 Ohms. High or open readings indicate a harness or servo fault. Go to step 7. If voltage is present, with the engine at idle and using a paper clip, jump the White/Pink wire to the Grey/Black wire. Next, hook a jumper wire to the paper clip and MOMENTARILY tap the other end to ground. The engine should accelerate rapidly. If there is no change, go to step 7. If OK, replace the AMP and retest operation.

To test the servo resistance, remove the connector and locate the terminals that the Orange/Yellow, White/Pink and Grey/Black wires connect to. Using an ohmmeter, recheck the servo resistance using the values listed in step 6. If OK, repair the wire harness concern. If servo resistance is out of range, replace the servo. If directed here from step 6 due to no acceleration but resistance values are OK, test for manifold vacuum to the servo. Locate the vacuum hose leading to the dump valve on the brake pedal and verify it is sealed. If all OK, replace the servo or cable and retest.
Daily Driver,1994 Auto,4.0,2wd, Extended cab. 162K
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