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My '99 STS is in the process of driving me crazy. I love the car but it's not drivable for the last week. I've had numerous suspension, stability and ABS codes in the last 30 days. Now the ones that come up regularly are; C1780, C1783 and C1785. Can anyone tell me if any of these or C1288 are enough to put the car in a permanent "limp mode"? The car will start and idle just fine, but any acceleration, moving or not and it stumbles and usually dies. For a few days it would move if the throttle was feathered but it was running so rich it was just sucking up the gas. For a while the ABS and traction control lights would come on, then it would have no fog lights, auto dark mirrors, rear defroster, HVAC controls and about half of the power steering was out. Any ideas??? Help Please!!!

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I would disconnect the battery and check the terminals, be sure there is no corrosion inside of the boot that goes over the cable ends. then hook back up and start the car. If problems are persisting pull all codes via the IPC and post them here. Welcome to Caddyinfo. You have come to the right place

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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My car has service suspension system, and stabilitrac all the time with no effect on drive-ability. Just lately I started getting abs, traction control as well. Two things seem to have happened. Motor mount broke and let the engine move a lot. Possibly because of that (don't know for sure) my radiator hose on the driver side started leaking where it clamps on the radiator and coolant was landing on the wiring connector below it to by the abs pump. I just found this and got the leak stopped and reattached the connector and abs and traction control lights are gone. The other two are problems with the struts and expense I am not ready to deal with. I suggest at least checking that connector. You will need to remove the lower plastic cover to see it, directly under the air box. If your car is running rich, you likely have another issue there.

I am not the first to have issues with that connector, especially if the clamp is not on it. Check the battery also like suggested above.

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Thanks for the input guys. The latest is; the batt. and connections are fine, the ABS and traction control lights are back on, the car runs the same(idles ok but any throttle at all it stumbles and dies). The current codes are; IPC-U1255, PCM-P1602, SDM-B1121, B1126, B1328 RSS-C1736, C1780, C1783, C1785. Anybody have any ideas? Tomorrow I'm gonna start opening wiring harnesses and looking for the open data lines and short circuits. Thanks again for any help.

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Okay, where are all the experts when I need them? Nobody has any ideas for a quick fix on this problem? I'm running out of hair to pull out(not that I had any to spare!) And I'm getting really tired of borrowing my daughters Ford, somebody please help!

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I don't have the time to go look up all the code definitions.

Do any of them relate to the catalytic converter?

A bad or clogged cat will let it start and idle but sometimes won't let it get much above idle.

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U1255 Class 2 Communication Malfunction (Serial Data Line Malfunction)
P1602 Loss Of EBTCM Serial Data
B1121 Driver Deployment Loop Resistance High
B1126 Driver Deployment Loop Open
B1328 Vehicle system voltage is greater than 15.9 volts
C1736 Compressor Relay Short to GND/Open Circuit
C1780 Loss of Steering Position Signal
C1783 ICCS2 Data Link Left Output Short Circuit to GND
C1785 ICCS2 Data Link Right Output Short Circuit to GND

None of these relate to your power and "stumbling" problem. Any engine or transmission problems will be reflected by Pnnnn codes. The only one you have relates to the EBTCM. The "Limp mode" is an overheating mode that runs the car on four cylinders at a time, rotating them while pumping cool air through the unused cylinders for cooling, and is good for about 50 hp. You are having a miss on acceleration and that isn't the same thing.

The EBTCM is the module bolted to the brake manifold, which has the ABS pump on it. That module is where TCS, ABS, and ICCS2 (Stabilitrak) live. One of the things that the EBTCM does is send a "requested torque" signal to the PCM, and the P1602 signal is saying that it isn't received when expected. The U1255 is from the IPC, but when it throws a U1255 it's usually a problem with communicating with the EBTCM.

I would start with the air bag codes. The air bag in the steering wheel apparently is disconnected, as shown with the B1121 and B1126.

The B1328 is a bit disturbing. It means that someone has put a fast charger on the battery while it is in the car without disconnecting it. Those chargers can put a voltage on the whole car that is high enough to fry everything. Apparently the modules are still working, though. Just don't use a fast charger on the battery while it is in the car and connected.

The C1736 apparently refers to the compressor that is part of the leveling system. You can look for that after you get the other suspension codes fixed.

The C1780 code means that the steering wheel position sensor output isn't getting through. It's probably disconnected or the connector is loose. You have to fix that or you will get "Stability reduced" and "Speed limited to 80 mph" messages.

The C1783 and C1785 signals are telling you that the road force signals from the RSS aren't getting to the EBTCM. Sometimes these codes, along with the U1255, C1780, and P1602 codes mean that the EBTCM is down. The place to start with all these codes at once is the "Brake" fuses, 10 Amp and 50 Amp maxifuse, in the underhood fuse and relay center, and the EBTCM connector.

All of the other problems, no power, stalling, dark mirrors, no fog lights, and such indicate a battery or battery cable problem.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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It would be simple enough to rule out the cat. There are 4 studs with nuts that connect the cat to the exhaust manifold down pipe, directly under the console. A 10mm wrench will remove them and a large screw driver/pry bar will be needed to pry them apart.

I would have a new gasket handy and spray the nuts with the best penetrating oil you can find, the day before, and use a 6 point socket or wrench, they are likely to be rusted.

If the car will run after unhooking that, the cat is plugged.

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except if you live in NY and have rust issues. then 10mm becomes whatever gets it out lol.

My flange bolts broke on my 96 because of the lovely rust.

Very good way to test the cat given you remove the flange before the cat

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Thanks Cadillac Jim, for giving me a place to start. I'm sure I'd probably have a more functional brain when it comes to cars(I wrenched on them long enough) problem is it was a hundred years ago, almost. There were no computers or modules or anything else, just timing, dwell and your choice of two things to win races; cubic inches or cubic money!

I see Jim that you have a CTS-V, with that car I could die happy. The local dealer here said they'd give me $7500 for my STS on a trade(I only paid $3800 for it), problem is the CTS-V is $73,000 and it would outlast me and I'd have payments of $3000 a month. So I'll continue to drool when I drive by! Thanks again Jim, I'm gonna get my flashlight and get started now(it's midnight here).

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Get a used one, just check the CarFAX or equivalent first, and get a dealer to check its history by VIN. If it hasn't been on the track, it is hard to abuse one on the street. The supercharged version has been out there since the 2009 model year, and all of them, even the 2014, are 556 SAE hp.

If the CAT is bad, you usually get a P0420 code, but not always. A high-end scan tool can look at the waveforms on the oxygen sensors on the cat and see quickly if the cat is bad, though. There is a comb shape to the waveform in front of the cat. If the waveform on the back of the cat has the same shape, the cat is bad. The waveform out of the cat should be much smoother than the waveform in; the teeth of the comb will be far shorter and spread out a little bit, unless the cat isn't lighting off, in which case it will be the same as the intake.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Just a quick thank you to all who responded to my problem. I haven't attempted the suspension problems yet but, the acceleration/stumble/stall thing was the cat, I unbolted it and slapped a length of tubing in it's place, and OMG! A little loud but the old girl was back to her old self(smokin' the tires and chewin' up mustangs!) Sorry ford guys but it's a true story.

Thanks Cadillac Jim for your input, although I'll still drool when I see a CTS-V it looks like I'll be driving this old Silver Shark for some time to come. Good night all.

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