steveb

Help! Can’t fix my cruise control. I've pulled my driver side battery out so many times this week to get to the servo that my back is out. Finally pulled the last strand of my hair out tonight and now I'm bald.

Short Story:

Looks like an electronic issue. I found I don't have 12V from the PCM right after I engage the Cruise with engine idling. Cruise light does come on momentarily.

BUT if I unplug the brake light connector I have 13.8V fine on pin 3 (yellow / red stripe wire) when I engage the cruise with engine idling.

It’s only after I connect the brake light connector and engage the cruise – that my voltage is gone. I have the servo unplugged just measuring in the connector. My digital meter jumps for a split second but measures nothing as if I have a short somewhere.. I’m lost?


-------------

Explicit Details:

Cruise control went out on me last week. Figured it was the vacuum hose spot I patched last time so this time I ran a WHOLE new vacuum line to the servo. Didn’t fix it.

Driving down the road the Cruise light DOES come on when I press the button but cruise won’t engage. The cruise light will stay on for a few seconds then shut off. It will not illuminate again unless I shut the truck off, restart it and do it all over again.

I have no 12V on Servo connector Pin 3 (dark blue / red stripe) while engine is running and I’m pressing the Cruise button (light comes on for a few seconds but goes out). I’m measuring this with battery ground and the servo connector unplugged.

Back tracked to the brake light switch. I unplugged the connector to it, cranked the engine and checked pin 3 (Yellow / red stripe) with engine running and pressing the cruise button. Cruise light illuminates and I get 13.8V there and it stays. Grabbed a new switch from the auto parts store right before they closed, plugged it in but I’ve got the same problem.

I have continuity from the PCM pin 11 (yellow / red stripe) all the way through the brake light switch onto my servo connector pin 3 (dark blue/ red stripe).

Checked for ground on servo pin 4 (black) and found a funky reading leading me to believe I had a bad ground. Tapped the wire and grounded it to the chassis where the battery connector is. Cruise still doesn’t work, same missing voltage.

Figured the wire from the brake light switch to the servo was shorted somewhere because with that brake light switch unplugged I’m getting voltage from the PCM fine. So I cut and ran a new wire from brake light switch pin 4 to the servo connector 3 (replacing that dark blue / red stripe wire). Verified continuity. Same problem!! I can engage the Cruise light but voltage is there momentarily and disappears. Again if I unplug that brake light switch and measure the PCM wire voltage stays.

I’m lost. Doesn’t make sense to me unless the PCM is killing the circuit for some reason? If so, why do I have voltage OK when that brake light switch is unplugged?

I’m a hair shy of just tapping 12 volts directly to the servo on pin 3 and heading out like a test pilot but I’m afraid to damage the PCM or something.

What am I missing here? All other gauges are fine. No trouble code light. No ABS light. Brake lights are working...???

steveb

I'm on to something with that brake light switch.

I unplug it tonight and stab a temporary jumper wire across pins 3 and 4 in the connector and I have 13.8V constant when engine is idling and I press the Cruise button. This is with the servo plugged in under the hood.

So basically my problem seems to be a short in another circuit that shares wiring in the brake light switch that is killing the 12V going to my cruise. Continuing to research...

Busboy

The brake lite sw has 3 sets of contacts, 1 for the brake lites the other 2 sets for the cruise. Just change the brake lite sw. I use a chrysler brake lite sw on another 4X4 and just had to change it, I took it apart to see what the problem is with these sw's. Well the contacts are not flat on these sw's so the contact area is VERY small and soon pit causing bad continuity.

steveb

Ran out of patience, gave up and took it into the shop. WAS the cruise servo after all.

Basically if your cruise doesn't work, if you know battery acid didn't ruin your vaccume line, your cruise light comes on for a while when you attempt to engage but cruise doesn't engage then the cruise light goes off, there are NO CODES thrown (here's the key), and your airbag light isn't shining and nothing else is wrong as if you'd suspect clock springs in your steering wheel ... just haul off and replace the servo.

If I did that it would have saved me about 80 bucks. The factory service manual said to apply voltage on one of the servo pins and you should read voltage on the other pins. I didn't do this, just checked for continuity and I HAD continuity across the pins so naturally I would have had voltage (the book doesn't say how much voltage though) so I ruled it out. Hope I save somebody the 80 bucks I wasted along with the frustration.