diagnose 2001 XJ cruise control problem

Hey guys, trying to get the cruise control working on my old XJ. My brother owns it now after I switched to the darkside, and I'm trying to get it working for him. 2001 XJ, 4.0, AW4, NP231, 8.25 rear, HP30 front, 6.5" longarm, 125,000 miles.

The cruise servo locked up one day, kept the throttle open and accelerating. Had to kill the ignition and unhook the cruise cable from the throttle body. A few months later, got around to replacing the servo with a NOS unit and now we've got nothing. Checked for vacuum leaks, none. Checked for resistance in the cruise cable, it's fine. Put the old servo back in, still doesn't work. Re-installed the NOS unit since it's newer and non-returnable.

Cruise light does light up when the "On/Off" button is pressed. However, pressing the "Set" button (tested between 40-55mph) has no reaction. After this, switched back to the original servo, and same thing. Searched online a bit, and found this thread: http://www.naxja.org/forum/showthread.php?t=1038194 and grabbed my meter to test the circuit resistance. Compared to those, my switches match except the "Set" and "Resume/Accel" switches. Those come in with drastically different values. (4300 vs 7000ohms for Set, and 8900 vs 15000 for Resume) I tested these with the switches removed from the steering wheel.

Based on the meter readings, I assumed bad switches and ordered a set on ebay. Those came in, tested before install and got the exact same results. Ok, strange... installed, out for a test drive and same thing. Cruise light works, nothing else.

Rather than mess with ebay more, I checked with my local club and a guy has an entire steering column out of an 2001 XJ. Said the cruise worked before parting it out (after wrecking it, airbags did not fire). Pulled the switches and tested... same values as mine and the ebay set.

Ok, backstory out of the way... the FSM I have does not have any resistance values listed for those switches. But, checking the factory parts catalogs, both 1999 and 2001 use the same part numbers for the switches and wiring. (56007530AD right, 56007531AD left and 56009437 for the wiring). Can I safely assume that all 3 of the switch sets that I've tested are all bad, and failed in the same manner?

I still think that all 3 switches might be bad, and will try to find a NOS set.

Assuming that somehow the switches are fine (and my two meters are bad, or the published values are wrong), where should I look next? Since the "Cruise" light turns on, I assume that the clockspring is fine... otherwise the computer wouldn't properly get that 500ohm signal. Moving on from there, brake light switch... if that was bad, wouldn't the brake lights be on (or not come on at all)? They seem to work properly. Already checked for vacuum leaks, what else can I try?

A scan tool that can read live data should have PIDs for the cruise.. you check switch function there.

IIRC, The cruise uses a different circuit on the brake switch, separate from the brake lamps.

My scan tool is a basic code reader, sadly. Hmm, I'll see if I can find a schematic for the brake switch.

FYI the switch ohm values for the 00-01 is different than the 97-99. I don't know what they're supposed to be as I've not done any research on it in several years, but when I was looking to put cruse on my 00 I remember reading in several places only 00-01switches would work. As far as the actuators I'm thinking they're all the same from 97-01, but maybe they're different electronically.

The servo's never really changed at all. Early HO servo's can be swapped for a later servo ... Etc... I have a ZJ servo in my 00.
The steering wheel switch resistance values did change, 99 and earlier used a different resistance than the 00+.
When my cruise failed to function, it just stopped, turned out it was a faulty brake switch. Cruise light came on/off but nothing else happened. Once in a blue moon it would come on for a minute at most. Very rare though.
Before I found my issue I swapped switches in the column, clockspring (so now I have a good used spare), servo, and went over all the wiring.
Swapped the brake switch and it's been working ever since. Turned out the one I installed a year before was faulty only on the cruise circuit.

Sent from my SGH-I337M using Tapatalk

Devilfrog said:

The servo's never really changed at all. Early HO servo's can be swapped for a later servo ... Etc... I have a ZJ servo in my 00.
The steering wheel switch resistance values did change, 99 and earlier used a different resistance than the 00+.
When my cruise failed to function, it just stopped, turned out it was a faulty brake switch. Cruise light came on/off but nothing else happened. Once in a blue moon it would come on for a minute at most. Very rare though.
Before I found my issue I swapped switches in the column, clockspring (so now I have a good used spare), servo, and went over all the wiring.
Swapped the brake switch and it's been working ever since. Turned out the one I installed a year before was faulty only on the cruise circuit.

Sent from my SGH-I337M using Tapatalk

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You know come to think of it the cruse in my 99 was acting up a while ago, and I think it was doing the same thing (light would come on, but nothing happened). IIRC I readjusted the brake switch, and I'm thinking that fixed it.