tylerwerrin

Hi guys,

I still can't get the damn cruise control to work in my T56 inspired XJ6. Here's an update on what I've tried to do to remedy the situation -- maybe someone can chime in:

I've updated my wiring schematic to best reflect my set up now:

https://dl.dropbox.com/u/24984984/GM...0XJ6_Color.jpg

I based my wiring off this PDF, which is reflective of the stock wiring in an LT1:

https://dl.dropbox.com/u/24984984/Cr...T1%20Stock.pdf

Here's a schematic for the XJ6' brake light circuit, in case anyone gets confused about the CHML circuit:

https://dl.dropbox.com/u/24984984/XJ...%20Circuit.jpg

What I've done so far:

1. I have wired in a CHML from a 95 Z28 with two new 921 bulbs. Cruise is Still not working after this mod.

2. Reconfirmed the wiring all around using this checklist:
A) Ignition off, Cruise Master Switch Off – No voltage at cruise module terminal F, no voltage at Cruise Master Switch (CMS) LGY or B terminals, no voltage at either side of SET Switch.

B) Ignition On, Cruise Master Switch Off – 12V at cruise module terminal F, 12V at Cruise Master Switch LGY & B terminals, no voltage at either side of SET Switch. With the brake pedal up, there should be 12V at cruise module Terminal D, and no Voltage at cruise module Terminal G. With the brake pedal pressed, No Voltage at cruise module Terminal D, and 12V at cruise module Terminal G.

C) Ignition On, Cruise Master Switch On – 12V at cruise module terminal F, 12V at CMS LGY, B, & YO terminals, 12V at cruise module Terminal A, 12V at Set Switch Terminal BK.

D) With Ignition on, and Cruise Master Switch on as 3 above, when SET Switch is pressed, then, and only then, should you have 12V at cruise module Terminal B. When Cruise Master Switch is held to position 3, you will have 12V at cruise module terminal C.

E) With the brake pedal up, no voltage on either side of the SET switch until the Cruise Master Switch is turned on – then you will have 12V at the cruise master switch YO Terminal, the BK side of the Set Switch, and Terminal A of the Cruise Module. You will have 12V to BS of the Cruise Master Switch, and Cruise Module Terminal C, only when the Cruise Master Switch is held to position 3.

All of the above steps checked out.

3. Picked up another Cruise Module at the junkyard to see if my cruise is faulty. I haven't tested it yet.

4. Probed for the VSS signal (terminal B8) at the PCM & at the cruise module Dk Green/White wire (terminal K on cruise module) -- still getting odd readings (11v key on, 12.4 engine running) when I should be getting 6.5/7.5v. However, the speed of the car has been verified to be near the correct speed using TTS Datamaster and Freescan.

Anyways, that's where I'm at now. If anyone can help me out, I'd really appreciate it -- not sure what is missing, or what could be wrong!

Tyler

ACE1252

It may be this weekend before I can dive into this and give you detailed schematics from my 1996 factory manual, but I did glance at yours and my 96.

Is the brake input("G") pulled low except when you press the brake pedal? Based on what I see from your schematic, the module(internally) may be putting 12V to the brake input("G") all the time which would keep it from working. Basically, I think your CHML is wired to the cruise module wrong. The factory manual states this......

"Important! Brake Signal input must be pulled low thru center high mounted stoplamp bulb or cruise control will not work."

http://www.ace1252.com/images/Jag_LT...se_problem.JPG

I simply showed "only" a bulb with no connections from the brake switch. Be sure to wire it to an actual brake lamp or you might have a "safety issue" of some type with the module doing something unexpected if you wire it straight to ground. I'd hate for the car to run away without being able to stop it....I think the other brake input would stop it, but I don't know how the module is programmed....better safe than sorry.

Using an actual brake tail light of your car(don't try to simulate for safety sake), just splice in a wire from the "top" of a brake lamp(non-ground side of lamp!! be on the "switched" side of lamp) to Brake Input("G") as I've added to your schematic.

Also, if you are not using traction control, then the Low traction lamp stuff is not necessary and it's just 12V provided through the clutch anticipate switch and brake switch(both in series) to brake input("D"). Should be 12V to this input all the time until you press the clutch or brake.

If the above does not solve the problem, I'll try to put together a state chart based on what I see from the schematic.

bobdec

Tyler item number 4 in your list.. PCM pin 'B8' is called the "VSS Output" signal in the documentation, but it is NOT the VSS Output. VSS feeds the PCM pins A31 & A32 with analog signal from the sensor. The PCM converts VSS depending on rear and tire info into a 4K pulse per mile DC pulse signal to the dash cluster (speedometer) and also sends the signal to the ABS module and Cruise Module. You can have correct speed in the PCM and still have a bad signal level on pin B8. The service manual says the pin B4 circuit s/b 6.5 ignition on engine off and yours reads 11.0 volts. However in your setup you pin B8 feeds the Dakota converter box and the Cruise Module. I have Never scoped that line , but if the svc man says 6.5V w/o any VSS input to the PCM then the 6.5V in the svc man must be with no 4K DC pulse signals. From that I suspect a bad termination of the circuit. In the F-Body my guess is the dash cluster would provide correct termination as the Cruise and ABS can be removed and the speedometer would still work. Maybe the Dakota box is recognizing and doing a correct conversion from 4K pin B4 pulse to your Jag speedometer. But not terminating the B4 circuit down to 6.5 volts. Cruise may be looking for a TTL level. Maybe impedance in the Dakota is to high for the PCM driver. Shooting this w/o an oscilloscope and comparing a working circuit and yours is getting tricky. if I can free up later on today I will put my scope on the B8 circuit, jack it up and see what the static and then wheel spinning signals on B8 look like. I've done this before for pulses per/ms data, but never recorded the voltage levels !!. Have not looked at any of your schematics yet ACE1252 seems to have a good grip on that.. This has my interest..

tylerwerrin

Thanks for helping guys!

Ace:
Being "pulled low", I tried to mimic the circuit for the Z28, which is that the light blue (or yellow indicated in the schematic) wire from terminal "G" of the cruise module is tapped into the Green/Purple wire of the XJ6, which feeds the rear stop lamps. When I step on the brake, the circuit closes and I get power to the lamps.

I wired up a CHML (the actual one from a z28, 2 "921" 18 watt bulbs, inside the lens) in the trunk to mimic how the Z28's CHML would function. I verified that the CHML lights up when I press on the brakes. The one thing that's different regarding the CHML circuit is that it on the stock schematic, the 12v source is "always on" (stock camaro), direct battery feed whereas mine (xj6), the key has to be on. In the end, the circuit works the same though, as it closes when I depress the brake pedal. In looking at the diagram you posted, I think that is how mine is set up now. I'm not using traction control, btw. If you look at the XJ6 brake light schematic, you can see where the CHML wiring comes in. I also updated my schematic to show the other half of the CHML circuit a bit more clear:

https://dl.dropbox.com/u/24984984/GM...0XJ6_Color.jpg

You can see where I tapped into the "Green Purple" wire (Terminal G) -- after the NO "Brake Lamp". The CHML lights when I press on the brake pedal.

Bob:
When you said "B4" terminal, I assume you meant "B8"?

http://shbox.com/1/1995_pcm_conn_b.jpg

As for the VSS output circuit to the speedo, I was thinking the "dakota box" has something to do with the signal as well -- perhaps queering it in some way to give me the funky voltage readouts at the PCM? I'll try removing the dakota box from the equation by just running a fresh wire from "B8" directly to the cruise module and see what happens -- either that, or disconnect the dakota box from the circuit. What is a "TTL" level, by the way? Thanks for checking it out on the scope for me bob - it'll be really helpful!


Thanks for the continued help guys!

ACE1252

Tyler,

I did miss that part. I was concentrating on the '95 schematics.

The main thing is to make sure that brake input G is pulled low by the brake lamp. It appears to be the way you have it, but make sure by probing that terminal with a voltmeter with the motor on and the cruise switch on. It should read 0 volts.

The cruise simulation would be interesting to try. I may try that along with you Bob and probe around to see what the signals are.....

I have read in the manual that the cruise will not operate below 25mph. So any testing may need to be with the speedo turning faster than that. I'm also not sure if it will work based on the front wheels being at zero speed. The programming may not allow the cruise to work without them at close to the same speed as the rear. I know when there is a difference between my fronts and rears the Low Trac light will come on....not sure how it will effect cruise. Does raise an interesting question.....if one of the wheel speed sensors fail...will the cruise still work?

Many also need to know if there is a phase difference between the VSS hi and low signal(I'm not sure how either of them look...but I'll try to find out).

Oh, one more question...the HMBL on the XJ6...is it LED or a light bulb?

bobdec

Corrected my post to read B8 not B4.. So much for believing books.. Ignition on & engine off B8 reads 10 volts not 6.5 as the book says it should, my battery is 12.7 w/ign on eng off so basically it reads 2.7 volts below bat voltage. Jacked up one wheel and w/ ign on and engine running & spinning speedometer at 10 MPH B8 swings from +11v up level to negative pulses going to 0V, nice square wave. Put a high impedance DVM in AC mode on the line when running 10 MPH and line reads 10.8 volts remember in AC the frequency of up Vs down will effect the AC voltage reading.

tylerwerrin

Ace:
For the cruise simulation, are you referring to the diagnostic check where you put your foot on the brake for 10 seconds, hold down the set & master switch to ON and then release the brake? I've tried that one, to no avail. A friend of mine tried the simulation in his 97 Z28 and it didn't work, yet his cruise works while driving.

I'll try probing the Terminal "G" on the cruise module to make sure it reads "0 volts". Also, just to make it extra clear about the CHML (the wiring schematic might be confusing), the CHML spurs off the GP wire BEFORE going into the "Bulb Failure Unit" -- I did this because my model XJ6 doesn't have provisions for the CHML (it came on a model a couple years later). However, it's function should remain the same -- i get 12v when the brake is depressed -- since my tap in is before the "bulb failure unit", I don't think the voltages are getting messed with. The CHML (HMBL?) is the unit taken from a 95 camaro -- i also have an XJ6 one I haven't installed yet. The Camaro uses 2 18 watt "921" bulbs -- not LED. The XJ6 unit uses 4 3.78 watt bulbs (194 i think) wired in parallel, also regular light bulb.

Bob:
It sounds like your readings are close to mine for the VSS! I guess this is good news, as it looks like the "dakota box" isn't queering the signal from the VSS output from terminal B8. However, it still is odd that we are getting the readings we are. A few other forum posts i browsed through had numbers similar to the book. It sounds like VSS might be ruled out for now, but I'll try running a new wire from the B8 terminal to the cruise module just for giggles.

Is there a way to be sure my brake input for terminal G is being "pulled low"? I know that the CHML lights when i step on the brake, and I know that the wire connected to terminal G is tapped into the "GP" wire which feeds the CHML & rear stop lights.

bobdec

Your actual wiring schematic may be confusing as it implies Curise Module terminal 'G' is going through the Jag 'Bulb Failure Unit' . The 'Jag XJ6 Brake Light Circuit' schematic actually shows Wire from Cruse Module 'G' is connected to terminal 'B' on the failure unit and the another wire on terminal 'B' goes to the center light positive lead. So in actuallity wire 'G' is NOT going through the failure unit. Is that correct ???
As far as pulling to 'G' to ground. If your DVM has a low amperage range you can check current going through the blue wire with ign on brake off. My guess is current s/b in the low single digit milli amps. Also another test....This test will only work if pin 'G' is floating above ground. With ign on brake off you can try pulling the blue wire off of terminal 'G' at the cruise module and using a DVM with high impedance measure the voltage level on pin G at the module. It may be very low so try all voltage ranges of the meter. Hopefully it will be at a level higher than OV. Then check the end of the disconnected blue wire and verify it is the 'exact' voltage level of chassis ground s/b 0V. Then attach blue wire to 'G' and insure 'G' is now at chassis ground voltage.

tylerwerrin

Bob:

The bulb failure unit is tricky to explain in schematics, but I'll try:

The Light Blue "Terminal G" wire taps into the Green/Purple (GP) wire AFTER the NO brake lamp switch. The GP wire then travels to the rear of the car, where it is connected to a multi pin connector (don't have a picture right now, I'll take one at lunch), which connects to the bulb failure unit:

https://dl.dropbox.com/u/24984984/Bulb%20Failure.JPG

The GP wire is the energizing wire for the 2 brake stop lamps, which are connected to the bulb failure unit. If you look at this schematic you can see how the brake lights come off the unit:

https://dl.dropbox.com/u/24984984/XJ...%20Circuit.jpg

I mentioned above that my particular XJ6 doesn't have provisions for a CHML, like this schematic shows. Instead, I tapped into the GP wire BEFORE the bulb failure unit. My setup looks like this:

https://dl.dropbox.com/u/24984984/XJ...t_Modified.jpg

You can see that I just tapped in (for the CHML) before the "B" terminal on the bulb failure unit.

Hopefully that makes sense. Ace suggested wiring the CHML right off the blue wire in the cab, which i could also try, but i don't see how that'd change anything. I wish i could just eliminate the bulb failure unit altogether to eliminate it as a potential problem -- i was thinking of just switching to a relay, which is effectively what the bulb failure unit is, but I'm not sure which to use.

As for the tests you mentioned I'll give em a try today at lunch. I can also snap some pictures for visual reference as well.

tylerwerrin

Ok, results from probing:

Bob:
With the CHML DISCONNECTED, after stepping on the brake pedal, my DVM read at the light blue wire was .6mv. I reverified with several different ground points, including the ground point for the cruise module.

With the CHML CONNECTED, my DVM read is .3mv:

https://dl.dropbox.com/u/24984984/DVM%20Read.JPG

After a few minutes I retested the same wire after stepping on the brake, and it read .6mv. Hmm, interesting. I snipped the light blue terminal G wire, and measured the wire with my DVM, coming from the cruise module -- it ready 9.72v with key on. With key off it read 0v.

I then measured other end, which goes to the GP wire and it read 0.0v. I twisted the Lt blue terminal G wire back together and measured again. Came back with .3mv. However after a few minutes I retested it and it was up to .6mv again.

I traced back to where I made my splice in the cab at the GP wire and measured there. The voltage was .3mv there as well. When I pushed on the brake, I got 11.58v with the key on, and the CHML & brake lights illuminated. I measured the ohms across the terminals on the brake lamp switch, and it read 0.0L. Finally, I probed the CHML in the trunk from ground to the GP wire, and came back with 0.0v!

So thats where I'm at now -- it seems as though there is an issue getting the circuit completely pulled down to 0v. Since the ground path from the GP wire to the trunk seems good, and the ground from the cruise module is good, I'm not sure where the problem is coming from. It's very confusing.

ACE1252

0.3mV and 0.6mV is more than close enough to be considered zero in this case....think about it....that is 0.0003V and 0.0006V. Heck, 0.2V or below should be good(maybe even a little higher than that....).

Is the above what you get with the CHML wired to the "G" terminal? Sorry that I may be asking a question you've already answered, but I just want to make sure I understand. The part where you measured 9.72V has got me a little confused. Did you removed the CHML wiring from terminal "G" to get that reading at terminal "G"?

How are you controlling the system(on/off, set/coast, resume/accel)? Are you using a turn signal stalk from a GM car?

Do you have the ability to scan the PCM? Are things like vehicle speed, voltage level, engine speed, and even gear range(I think this more for automatic) all reading properly from the scanner? I'm going to take pictures of all the factory diagnostic info I can find in the manual for you. The above are some of the things it's flagging to scan in the PCM.

The circuit operation mentions that "D" must change states once each ignition cycle before it will operate. Later production vehicles will allow it at either "D" or "G".

Edit:Promised Factory manual snapshots....

1996 F-body Cruise Control Electrical Diagnosis
http://www.ace1252.com/1996_Z28_Fact...cal_Diagnosis/

tylerwerrin

Ace:

The .3mv and .6mv readings I got were with the CHML wired into the circuit. The 9.72 volts I was referring to was when I snipped the Terminal G wire under the hood and just measured the voltage coming directly from the cruise module, without the CHML or any of the brake circuit tied to it. The 9.72 read came with the Key on. I measured the other side of the circuit (the other half of the terminal G wire tapped into the brake "GP" wire) and got a flat "0" volt reading. I know the .3 and .6mv readings are low, I just assumed it had to be zero. Thats good it doesnt have to be though!

As for the set switch and master switch, I am using the Jaguar stalk and the Jaguar master switch. If you look at my color integration schematic, I modified my master switch to be like the GM's master switch. I wanted to keep it XJ6 on the interior because everything already fit, etc.

I definitely use the brake more than once before getting to the freeway, or even a larger boulevard to attempt a cruise control test, so I think terminal G or D have their requirements made.

And yep, I've scanned/tuned the car countless times. It's one of the great things about owning an OBD1 car -- ease of tuning and ubiquitous tuning software. When I drove around with my laptop patched into the car, the MPH read close to what the speedometer was outputting, so I'm pretty confident that the VSS signal is a good one. Bob tested his VSS, and probed the PCM terminals and we have similar voltages so I think its not a problem.

Thanks for posting those pictures!

One other note:
My friend suggested that the capacitor on the XJ6 circuit could be causing the .3mv fluctuation. He also owns a converted xj6, however his is LS1. Since his is automatic, he used a DPDT switch for torque lockup and the brake lights. Is it possible the capacitor is messing with the signal somehow?

ACE1252

The cap might cause a problem it if is leaky. As they get older, they start "leaking"(drawing current). As best I can tell, it's there to help protect the switch contacts from arcing and such. You can disconnect one end of it, as a test, and see if it helps.

I will say, so far it looks like you've got the bases covered pretty good. I'll try to do some testing on my system and come up with a state diagram on what needs to happen as far as voltage levels are concerned on the inputs. The only thing we might not be sure of is timing or phasing of the signals.

Go through my schematics and troubleshooting charts(especially chart #1) with a fine tooth comb. You could be fighting a broken module. My only concern about swapping in the other one is if something is not right voltage wise on one of the terminals now, it might blow the other one.

Going back to the CHML's for a second, I don't think you need to simulate the bulbs of the F-body, but, out of curiosity, what is the bulb resistance of the F-body bulb compared to the resistance of your CHML? I don't think the resistance value is that important, it's just that ground needs to be seen by terminal "G" through the bulb.

tylerwerrin

I'll swap in the other module today and see if that does anything. As for the CHML, I'm using the camaro's CHML right now -- I believe the resistance for the XJ6 CHML is 1ohm, but I haven't measured it myself (I read it on another forum).

UPDATE:

I tried wiring the CHML in the different place, spurred from the lt blue wire. Nothing changed.

I looked through the manual and followed the entire trouble shooting process from beginning to end. The only place that seems different than what the book says is the VSS. The book wants 7v with the key on, whereas I'm getting 10.65/10.64. I noticed that the voltage fluctuated a bit a tiny bit (from 10.65 to 10.64 and back again), and my speedometer needle always had a little "jiggle" when at idle. When I disconnected the converter box, the voltage stayed at a clean 10.65, and my speedometer obviously stopped working. I drove about 40mph down the boulevard and tried cruise, but again no luck.

Finally I swapped out the cruise control module itself. I didn't swap the actuator motor, just the computer chip (the unit is designed like a clamshell, with the computer parts on the ceiling of the unit, which plug into the motor below.) Again no luck. Next I suppose I'll try swapping out the cruise motor. If that doesn't work, I guess I'll go to the junk yard again and swap my cruise unit out with another. I'll find it hard to believe that 3 units were faulty.

Anyways, that's where I'm at now!

tylerwerrin

For kicks I uploaded pictures of the two different cruise modules -- perhaps someone in the future will find them useful. The "25140793 J Module" picture is the original module I was using when I first posted. I believe it came from a 96 Camaro Z28. The "25140613 F Module" came from a 94 or 95 Z28 I believe, although I'm not sure.

None of the parts looked damaged from a visual inspection. Tomorrow I am going to try and carefully remove the cable from the original unit and put it on the "new" unit to see if the actuator motor is actually the problem. I wish there was some documentation somewhere about how to test the motor!

Pictures:
https://dl.dropbox.com/u/24984984/Cr...F%20Module.JPG

https://dl.dropbox.com/u/24984984/Cr...140613%20F.JPG

https://dl.dropbox.com/u/24984984/Cr...J%20Module.JPG

https://dl.dropbox.com/u/24984984/Cr...140793%20J.JPG

https://dl.dropbox.com/u/24984984/Cr...0by%20Side.JPG


I went through the trouble shooting guide in the schematics one more time. Again, the tests all were OK except the VSS signal being above normal (the book said i should be getting 7, I'm getting 10.65). I'm also going to try swapping in a different PCM to see if that has any affect on the VSS. We'll see. Any other ideas, Ace, Bob?