E028 - Transmission shop telling me its electrical - Cadillac Forum - Enthusiast forums for Cadillac Owners


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Old 10-20-2010, 02:43 PM
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Default E028 - Transmission shop telling me its electrical

My 88 Eldo Biarritz has recently been jerking slightly when cruising and it is stopping me from being able to smog it. Sometimes the jerk wont happen, and sometimes it will, but it is always random. When they do the 15mph test and the 25mph test its jerking too much to get the correct reading on the dyno. I am getting code E028.

I have taken it to 2 transmission shops. The first one was recommended by a few people and I am pretty certain that they are good. They took a look at it drove it around and ran the diagnostics. They told me that they believed the problem to be electrical.

I took the car to a little electrical shop, which charged me for a half hour of labor and sent me on my way saying everything seemed ok. I don't think they really looked at it like they should have because since then I have noticed a few frayed wires here and there. Took it to another transmission shop, showed them the diagnostics paper that the other tranny shop had given to me explaining the E028, and he said right off the bat that it was electrical.

Being so pissed off that every mechanic in the book was sending me the opposite direction, I decided to take a look at it myself. I noticed a frayed wire under the fuse box that plugged into what i believe to be the charcoal canister (I may be wrong) but it is a black cylinder under the fuse box near the left headlight. I spliced a new wire in there and it should have a good connection now (I dont think that had to do with my problem, correct me if it could).

I then unplugged the 5 pronged wire that goes into the tranny from the ECM that has 4 wires to it. All of them were reading 14v except for the tan/blk wire, which my haynes manual is telling me goes to the TCC. I suspected this wire to be the problem, so I ran an 18ga wire directly from the plug into the ECM. (I purchased a new plug from picknpull) I drove it around a little bit and it seemed like it had maybe fixed it, but the problem happens so randomly that its hard to tell. The check engine light had shut off after a few blocks so I had thought i had fixed it.

Well with my luck, this morning I got back in it to change out the thermostat housing and the light is back on, with the E028 being the bastard turning it on again.

So, i'm not sure what I should do here. Ive been looted by all these b.s. shops all for them to point fingers somewhere else. I really dont have all the money in the world to take it to a specialist. hopefully it may be something I can tackle. if anybody has any ideas please help me if you can. Im out of ideas as of now. Thank you very much in advance.
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Old 10-22-2010, 09:35 AM
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E028 is a 3rd gear/4th gear pressure switch code. This should have nothing to do with the engine jerking while attempting to do the smog inspection. The only thing it might do, as far as drive-ability, is keep the lock-up clutch in the torque converter from applying.
This code could be electrical, sure, but it is most likely a failed pressure switch. The pressure switches are on the valve body of the transmission, located behind the side cover.
The ECM sends a 12v signal to the switches anytime the key is on, engine running. The pressure switches are normally closed, grounding the circuit, and the ECM will see "0" volts on the circuit. When 3rd(or 4th) gear is achieved, the switch goes open, and the ECM sees a 12v signal return. The ECM is NOT seeing the 12v signal go to ground, or it is NOT seeing the switch go open when in 3rd/4th gear. There is no distinction on which way the switch may have failed...just that the ECM did not see a change of state from the pressure switch. The problem is most likely a failed switch, but it's also possible the internal trans wiring harness has a fault somewhere. If you go thru the trouble to pull the side cover off to replace the switch, it's best to go ahead and do both while you're there.
I can't believe a trans shop wouldn't jump on this fix...they must be really busy...

The E028 is the only code that comes up? If so, it just doesn't make any sense that that would keep the engine from being able to hold a steady rpm while on the dyno. The only thing I can think of that might be connected would be the ECM control of the timing...it will change when the trans shifts into 3rd/4th, for emissions purposes. That's really the only reason for the pressure switches anyway...to let the ECM know the vehicle is in 3rd/4th gear, so it will adjust the timing accordingly.
hth.

I could send you the troubleshooting chart this evening, if you would like...I'd have to do it from the house...I don't have the info here at the shop.
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Old 10-22-2010, 09:08 PM
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Thank you so much for the reply. Ive asked this question at numerous sites and nobody ever answered.

Its kinda weird, because I ran a new wire from the tan/blk wire to the same at the ecm, and since then the code has cleared completely (even from the history codes) and the car is running perfectly.

Only problem is now, I went to smog it, and they were able to complete the test, but my CO and HC were off the roof. The CO, Im suspecting, is due to a bad cat that I am planning on replacing. But the HC I'm not sure what could be causing this. I revved it up to about 3500 rpm for a couple seconds and noticed about a 2 inch puddle of gas that came out of the exhaust pipe. I know this is due to fuel not being fully burned for whatever reason.

I had just replaced the spark plugs about 5000 miles ago, along with the cap and rotor. I just did wires about a month ago, less then 500 miles ago. And Im not getting a misfire at all. What else could be causing this? I plan on checking the plugs on sunday to check if they are good, but if im getting this much fuel in the exhaust due to the spark plugs it seems like it may be bad enough for a misfire but i could be wrong.

And, is it true that if im getting this problem I should change the oil ASAP? I read on another site that it could be corrosive to the engine parts because too much gas gets into them.

THank you so much for the help.

Oh and BTW, if you could send the chart that would be great I really appreciate it.

Last edited by norfmo; 10-22-2010 at 09:10 PM.
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Old 10-22-2010, 11:09 PM
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It's strange that you say you ran a new wire on the circuit with the tan/blk wire...if memory serves, that circuit/wire is for the lock-up solenoid, not either of the pressure switches, which you had a code for. That wire/circuit(tan/blk wire) is the ground signal from the ECM to the lock-up solenoid. The solenoid gets it's power(12v) on another circuit, from the brake switch, under the dash. The solenoid is powered any time the key is on, and the ECM provides the ground for the solenoid when it is time for it to come on.
What the heck...as long as the problem is solved, eh?
I'll have to dig up the info, and get it to ya tomorrow.

The high HC readings could be caused by a faulty EGR valve, or the EGR vacuum solenoid, or anything else that would keep the EGR from functioning properly, including an intake manifold that the EGR passages are stopped up on...a common problem on the '80s era Cad engines.
What you see coming out of the tailpipe is more likely condensation, rather than raw fuel...if there was actually raw fuel dripping out like that, you would definitely have some drive-ability issues, and lots of black smoke.
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Old 10-24-2010, 02:34 PM
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Thank you for all the help.

What are some troubleshooting steps for figuring out if its the EGR or something else? And where is the EGR vac*** solenoid?

And are you pretty sure it seems like something EGR related? The liquid coming out smells like gas and has a black tint to it.

THanks again!
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Old 10-25-2010, 01:13 PM
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I sent you a message requesting an e-mail addy...did you get that?

btw..pretty much anything coming out of the tailpipe is gonna smell like gas...

I'm not there, so I can't tell you for certain if there is an issue with the EGR, but that's what it sounds like from your description of the smog test, in my experience.
If you follow the vacuum line from the EGR valve, you'll find the solenoid...they are usually pretty close to the valve itself. I can send you some EGR tests to do, if needed, but I still need an e-mail addy to do that. Please send me a P/M...I'm not a fan of posting e-mail addys on the forum pages for everyone, including spam-bots, to find.

Also...locating a Factory Service Manual for your car would really help, if you want to do as much of your own work on your car as possible. I don't like paying someone else to do it, either! They are usually available on e-bay, fairly reasonably. Just an idea....

Last edited by Adams' Apple; 10-25-2010 at 01:16 PM.
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Old 10-25-2010, 05:56 PM
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Ok bought a vacuum pump last night. I have a few questions.

I read that the vacuum line going into the EGR should have vacuum at 2000 rpm when engine warmed up. Mine doesn't have any vacuum at all, even as high as 3 or 4000 rpm. I think this may be where the problem is at. The vacuum hose isn't leaky either, it wasn't getting vacuum at the solenoid or at the end of the hose.

I tested the plug going into the EGR vacuum solenoid and it was reading 13v, so the wire isn't shorted. Should this be creating some kind of suction at these rpms and if so could that be contributing to my hydrocarbon levels?

And also, I noticed my idle rpm is at around 950. I think I read somewhere that it should be at around 550 for this car. Is that true and how should I test out where the problem is there?

One more question too. I wanna test the cat, but I don't wanna create an exhaust leak that's leaky when plugged up. What's the most efficient way to plug the pipes back up after i screw the holes?

Thank you for all the help once again.
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Old 12-02-2017, 05:42 PM
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The thread above is exactly the issues I have been trying to resolve for 8 months. The thread stop before problem was resolved. They were sending info to each other thru private e-mail (PM)
I have five issues that sound like from the above thread could be related.

Transmission shifting in and out of 3rd and 4 gear in a
jerking motion . Code E028
Failed emissions. (Carbon Monoxide) Over limit.
White smoke, liquid and unburned gas smell coming from tail pipe.
High idle at around 1050 RPM.
Miss at idle.
After engine warm up A/C not blowing thru dash vents. Low to no vacuum.

All these issues came up at the same time. 1988 Cadillac Eldorado.

Could you send me a thread related to the above thread?
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1987, 1994, 3rd, 4th, bat, caddy, cadillac, ecm, gear, harness, pressure, sls, switch, trans, transmission, wiring

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