[Thornybastard]

Hi all,

Here's another cruise control thread because I couldn't find any problems that matched mine.

My cruise control stopped working on my 1996 E300D. I took about a 40 mile road trip today and the darn thing wouldn't set. I'd push up to set the speed as usual but nothing happened. Took foot off the gas and pushed the lever up, but just got the expected deceleration. It worked as recently as a month ago, even on an 800-mile roadtrip. Beautiful, very precise CC. Today is the first time I've tried it since early/mid August.

Since I just pulled a new wiring harness, I thought maybe that had something to do with it and was above my pay grade, so I took it to the mechanic. He and his son-in-law assured me it had nothing to do with that. We checked the brake lights and they worked fine. We popped the hood and looked at the throttle and everything seemed to be in order. Son-in-law had a fancy acronym for the throttle-cruise-ignition assembly like EEIACC or something.

I do not get any warning lights on the dash for anything. All the warning lights come on when I wait for the glow plugs and go off as expected when the car starts. Computer is shot and won't talk to the diagnostics, so it's all best guesses based on experience. These two guys I go to are quite good and can talk you through a job on the phone or in person with very precise descriptions and many years of experience that get the problem and solution right the first time.

Since it was 3:30 on Friday afternoon, the shop said to come back next week and they'll poke around. Any help in the meantime? Maybe I can do it this weekend.

EDIT: After poking around here, figure I should mention (since odd things seem to be connected) that at about this time also, I lost the light on the temp guage and right half of tach. Time display dims too. Prior to that, the outside temp guage was already super dim when I acquired it, only visible at night.

Thanks,
TB

 

[mrboca]

Hello

If the mechanics are 100 percent sure that it is not the wiring problem, it could then be a switch problem, and in this case you would get a fault code (P1520) but not necessarily a Check Engine light, as it is not really related to the basic engine performance.

You could check the switch at the engine computer connector, but you would need a schematic for that.

Regarding the brake switch. It has two contacts. One is for the brake switch, the other is for the traction and possibly for the cruise control. So, just because the brake lights work (first contact), it does not mean the second contact is activated when you press the brake pedal.

Do you have ETC (Electronic Traction Control), or ASR (acceleration Slip Regulation) with your car ?

 

[Deplore]

Did you change the tires, or is one of the rear tire super deflated compared to other?

 

[Thornybastard]

Hello

If the mechanics are 100 percent sure that it is not the wiring problem, it could then be a switch problem, and in this case you would get a fault code (P1520) but not necessarily a Check Engine light, as it is not really related to the basic engine performance.

You could check the switch at the engine computer connector, but you would need a schematic for that.

Regarding the brake switch. It has two contacts. One is for the brake switch, the other is for the traction and possibly for the cruise control. So, just because the brake lights work (first contact), it does not mean the second contact is activated when you press the brake pedal.

Do you have ETC (Electronic Traction Control), or ASR (acceleration Slip Regulation) with your car ?
[/QUOTE

mrboca, thank you for your interest.
1. No codes because computer doesn't work. Tried 3 different diagnostic devises and squat.

2.Since I can't check the switch at the engine computer on my own, I'll mention it to the shop on Tuesday if it comes to that.

3. I have ETC, I believe. The light comes on when you turn the key, like all the other lights, but goes off when the car starts. So no problem there as far as I can tell. However, this is the first day I've noticed it and haven't been in any ETC conditions yet to see if the big yellow triangle comes on (loose gravel, wet roads, etc). I take it if the second contact is shot, the BLS needs replacing?

Thanks again!

 

[Thornybastard]

Did you change the tires, or is one of the rear tire super deflated compared to other?

Deplore, thanks for replying.

Put four new tires on the end of May/beginning of June. Cruise control worked fine. All tires are equally and properly inflated.

 

[mrboca]

mrboca, thank you for your interest.
1. No codes because computer doesn't work. Tried 3 different diagnostic devises and squat.

2.Since I can't check the switch at the engine computer on my own, I'll mention it to the shop on Tuesday if it comes to that.

3. I have ETC, I believe. The light comes on when you turn the key, like all the other lights, but goes off when the car starts. So no problem there as far as I can tell. However, this is the first day I've noticed it and haven't been in any ETC conditions yet to see if the big yellow triangle comes on (loose gravel, wet roads, etc). I take it if the second contact is shot, the BLS needs replacing?

Thanks again!

What scanners did you try ? Maybe the fused power supply issue at the OBD2 port ? Check fuses 17 (always on), and fuse 15 (on with key in position 2). Both are under the hood at the driver's side.

If the BLS is bad, it needs to be replaced of course.

Item 16 guides how to test the Cruise Control Switch.

STAR TekInfo

 

[Thornybastard]

Thanks again.

Looks like fuse 17 is ok. Fuse 15 I'm not sure about. Frankly it was hard to tell with any of the blue fuses if they were on. I even shaded the fusebox with the lid trying to see them with the key in various poitions, and I really couldn't tell with the blue fuses. I pulled 15 and inspected it. The fuse itself is still good.

Very much appreciate the tech guide, but afraid that's beyond my ability with tools I have. Looks like I need a voltmeter to apply to the numbered holes in OBD2 port. Is that right? I should probably acquire one if I'm going to be working on this car myself. It's not like the '83 300D!

 

[mrboca]

I provided the info for the mechanic. It is hard to back probe the wires at the computer connector without proper tools.

'Let us know the outcome after your mechanic has a look at it. Hope they will look at the OBD2 / 38 pin diagnostic port to find out what is going on with the ECU access. If you got the wires replaced, it is possible that the diagnosis wire is not connected to the OBD2 / 38 pin diagnostic ports. It should be easy to determine for the mechanic ( check if 12V exists between pin 4/5 (ground) and pin 7 (signal line)).

 

[Thornybastard]

I provided the info for the mechanic. It is hard to back probe the wires at the computer connector without proper tools.

'Let us know the outcome after your mechanic has a look at it. Hope they will look at the OBD2 / 38 pin diagnostic port to find out what is going on with the ECU access. If you got the wires replaced, it is possible that the diagnosis wire is not connected to the OBD2 / 38 pin diagnostic ports. It should be easy to determine for the mechanic ( check if 12V exists between pin 4/5 (ground) and pin 7 (signal line)).

OK, so, sorry for the late reply but I just got around to doing this yesterday since it wasn't critical and a lot of stuff came up that distracted me.

Turns out it was a vacuum issue. Ran down the list of things we all discussed here with my mechanic including the tires and fuses, error code, etc. They put it up on the lift and saw some bad vacuum hoses, thought that might be it, and replaced them. Now the cruise control works again. He declined to say which vacuum hoses they were, only that they replaced all the bad ones they saw. That plus an oil change, pre-trip inspection (fluids, tires, etc) and remounting a loose fog light cost about $265.00 (US). I was happy.

 

[mrboca]

The question is, can a scanner communicate with the engine computer now?

 

[Thornybastard]

The question is, can a scanner communicate with the engine computer now?

No. Haven't licked that yet. Probably have to replace the brain box, and It seems like an unnecessary expense since it is only a monitoring computer, no control systems like in later models, as I understand it. All the warning lights work aside from the "check engine" light.

I got a warning for low washer fluid that kept coming up, fast than I reckoned I was using it. Turned out to be right. Leaky seal on the motor, so I replaced that. Then same warning light a little later, so I replaced the sensor. Fine since.

Traction control light comes on when expected.

I don't feel like the computer needs replacing urgently, but if you think I'm wrong about that, I'd like to hear about it. Mechanic says if I have a problem, fix it, and if I can't fix it bring it to him.

Oh, and the far left panel lights have come back on. Don't know why, but glad they're back. Far right doesn't matter since I never take the tach that high.

 

[mrboca]

The IFI computer does a lot more than monitoring. It controls a host of solenoids, valves, transducers. Obviously it is working fine, and no need to replace it. I asked the question because it may be a wiring issue for diagnostic line from the module or a grounding issue. You would need a working diagnostic access, as it will be hard to find a problem if any of the solenoids / valves electrically fail, not detected by visual inspection.

 

[Thornybastard]

The IFI computer does a lot more than monitoring. It controls a host of solenoids, valves, transducers. Obviously it is working fine, and no need to replace it. I asked the question because it may be a wiring issue for diagnostic line from the module or a grounding issue. You would need a working diagnostic access, as it will be hard to find a problem if any of the solenoids / valves electrically fail by visual inspection.

Ah. Well that doesn't sound too hard to check out. I'll look into that. Thanks. My god what a font of knowledge you (and this forum) are!