P1602 Loss Of Ebtcm Serial Data
I have been hunting down a wicked electrical problem for the last few months, and finally resolved it last night. I want to document my experiences, symptoms, and solutions so that if anybody else encounters this problem in the future, they can save themselves a lot of money, and a LOT of frustration.Problem Background and SymptomsAfter finishing my timsert job and putting the car back together, I was getting the ABS and Traction Control lights on the dash illuminated. Also, seemingly unrelated, my turn signals did not work. This problem would be intermittent. Once in a while, the ABS/Traction lights would go out while driving, and 1st gear would return. Sometimes the turn signals would work, other times they wouldn't. When things were working right, I noticed a very weird correlation between when I would flick the turn signal stalk, that this would immediately cause the ABS/Traction lights to come on.
This relation was very key to solving the problem, something I wish I would have noticed earlier.I did lots of searching on the forums, and even found one other member with this exact turn signal EBTCM issue, but unfortunately he seemed to have never resolved it. I learned that many people had EBTCM issues, and they they tend to go bad on these cars.Scanning the codes on my car (1996 Seville SLS, OBDII), I was getting a current P1602, 'loss of serial data from EBTCM'. I got out my FSM, and meticulously followed the diagnostics tree in the manual to diagnose the problem. This involves a bunch of steps, which basically probes almost every connector pin on the EBTCM connector to check for continuity, shorts to ground, shorts to voltage, and opens. I ran this full diagnostic tree with my multimeter several times, and always came to the same conclusion at the end of the tree 'Bad EBTCM, replace unit'.Come to find out, these are $650 from the dealer brand new, so I scoured for one from junk yards and on ebay.
I found a used on on ebay, but they guy wanted $299 which I felt was too much for a used one. He is a forum member here, and he agreed to bargain down to a reasonable price (thank you!). I received the used EBTCM, assuming this would alleviate all my problems, installed it, and NO GO. Still not working.
I assumed I had just gotten a bad unit. I shipped it back to him, and he tested it in his car, and confirmed it was bad. So, he sent me a new one that he had tried out in his own car to make sure it worked before he sent it to me. Imagine my surprise when I installed it in my car and it still didn't work! At this point, I threw in the towel and gave up.
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I was planning to sell the car anyways, and would just take my losses selling it with a bad ABS/traction system.But, the turn signal issue was really bothering me, so I decided to try and trouble shoot that system. First things first, I got all new bulbs, and new flasher. Still nothing worked. I took apart the steering column and replaced the turn signal switch.
Kind of a pain, and it still didn't fix the issue. Then I decided to follow the FSM's 'electronics diagnosis' section. It starts by saying to probe the 3 wires going to the flasher module, check for shorts to ground, shorts to voltage, grounds, opens, AND reference voltage. My multimeter found no shorts, no opens, but I found something very weird in that my brown wire, which was supposed to be system voltage (12v), was only reading 2.3v. So I went in the trunk to access the rear fuse panel, and sure enough found only 2.3v back there as well. While I was back there, I checked all the other fuses since I had things apart, and found all of the other circuits with 12v, except for the turn signal fuse, and the console fuse, both with 2.3v.In the FSM, the electrical diagram for the turn signal wiring shows power for the circuit originating from one of the big Maxi-fuses (30amp) in the front fuse box under the hood.
Probing up there, I found the same thing, just 2.3v. Now that's weird, because that is coming RIGHT off the battery (almost), and that was fine at 12v. So, I pulled the fuse, and found a very slight green corrosive haze on the terminal contacts. I wire brushed this clean, re-installed the Maxi-fuse, and checked the voltage - it was now 12v, as it should be.Tried out the turn signals, and they work! But OH MY GOD. So was the EBTCM!! The ABS/TCS lights were off, and I could drive totally normal, no ABS/Traction lights, and use my turn signals.
And it worked continously, with no intermittent failures like before. I couldn't figure out why this EBTCM issue all of a sudden became corrected, until I found THIS diagram in the FSM:It shows that the 'Batt 3' 30amp Maxi-fuse actually feeds both the turn signal circuit, and the EBTCM main power, through circuit #300.Corrosion on the Maxi-fuse terminals must have been causing a high resistance and therefore voltage drop on this line. All of the wires were intact, with no shorts, which is why when I was doing the EBTCM diagnostic tree, everything checked out. In my opinion, a MAJOR flaw in that diagnostic tree, is that it never asks you to verify +12v on that pin feeding the EBTCM! It has you check for shorts to ground, continuity, and opens, but never queries adequate voltage.Now that my EBTCM is getting 12v, it runs. Of course the module would not operate properly on 2.3v!! I'm surprise it even operated intermitently at that low voltage, but when it DID, flicking the turn signal stalk drew enough additional voltage on that #300 circuit, to cause the EBTCM to turn off, and thus illuminate the ABS/traction lights.Who would have guess that the EBTCM and turn signals were so closely integrated power-wise.The moral of the story.
P1602 Loss Of Ebtcm Serial Data Center
If you have an EBTCM problem AND turn signal problem. CHECK OUT CIRCUIT #300! Check the voltage at the small ABS fuse and Batt3 maxi-fuse under the hood, and the turn-signal fuse in the trunk. If they don't have 12v, you need to trace down where the high resistance in the circuit is. Corrosion on the maxi-fuse was my problem. I pulled my hair out over this issue, and hope to save someone else the hassle in the future. Edited November 20, 2007 by jcobz28.
Well done and thanks to you for the feedback. You have assisted future readers with similar problems.Those of us with electrical/electronic backgrounds keep cans of contact cleaner and copper wire brushes within easy reach. The advancing integration of mechanical devices with digital controls lifts the importance of reasoned diagnostics to a whole new level.Again; well done.Well done post.It can happen. Oxidized fuses.Cadillacs are extremely sensitive to good grounds, good battery.And, the fuses just sit there for years. Sometimes just pulling the fuse and reinserting it. Wipes off the oxidation.Same on the PCM pins. 10-15 year old.Simple unplug / replug can wipe the pins clean.
Ebtcm Module
And fix the car. WOW and WOW again.
Many thanks for your complete detailed explaination. I have a friend who has had his STS in the shop since August with this exact same problem. It doesn't help much we are located in the Dominican Republic and there is no certified mechanic down here to tackle this problem.
After ordering may items over ebay and replacing just about everything involved in the Tranny and Engine controls this post was the needle in the haystack. Your post has saved one STS from a certain painfull death.Thanks again. The circuit ties into the turn signals if I recall correctly, not the running lights. But if it is a turn signal that you have out, and you have replaced the bulb, and things still don't work, then it could be the problem. The turn signal sockets on these cars are also known for going bad, so visually inspect the contacts on your turn signal socket to make sure there are no burn marks or melted plastic in the housing. Flick the blinker on with the turn signal stalk and use a voltmeter to see what type of voltage you are getting at the bulb socket contacts.
P1602 Loss Of Ebtcm Serial Data Chart
If you have less than +12v peak (it will alternate obviously. This is how it blinks) then you may have the same issue as I did. If so, just follow my diagnostic instructions above. Electrical demons are no fun.