: Service Engine Light Codes...Please Help

01-04-05, 01:32 AM
Happy New Year to my Cadillac compadres! I was wondering if you guys can help me with the following diagnostic codes and how i can go about fixing it. Thanks in advance.

PCM P0139 - Heated Oxygen Sensor (HO2S) Slow Response Bank 1 Sensor 2
(I know there are two types of o2 sensors fo this car, which one would i have to get for this location and where is the location for this one)

RSS C1738 - Exhaust Solenoid Valve Short to GND
(I dont have a clue about this one)

PZM B1558 - BCM EPROM Checksum Error
(No Clue)

Once again, any help would be greatly appreciated. Thanks and have a great day.

01-04-05, 04:13 PM
As for the O2 sensor, I believe bank 1 sensor 2 is the one before the catalytic converter. It seems to be the first one to develop problems in the majority of cases I know of. Probably needs to be replaced. You'll need to buy or borrow an O2 sensor socket from an auto parts store and the Bosch part number for that sensor is 13444. It'll cost you about $60-$100 and you'll save on gas and save your catalytic converter. (plus pass emissions tests) Pretty easy to do. You can't miss it. It's just before the cat and it's the only thing sticking out of the exhaust pipe with wires attached to it. Disconnect the wires, take it out of there, stick in the new one, hook it up, you're done.

The exhaust valve solenoid short to ground is another common problem with the Electronic Level Control system. It's above the rear axle. There is a motor and pump to pump air into the rear shocks and a solenoid and valve to let air out. The solenoid tends to get wet, and therefore rusts, shorts out and pops the ELC fuse, and results in the code you see. While it's dead, the auto level system isn't working, so if you fill up the trunk with heavy stuff, the bank end is going to sit low. With ELC working, it rides better under those circumstances and it'll level itself out unless you fill up the trunk with lead or the ride height sensors are messed up. I've fixed mine before. What you're looking for is an ELC vent solenoid, or it might be called an automatic level control compressor or solenoid. If you can get the solenoid separately from the compressor, it will cost a lot less. The compressor/solenoid combo was about $400 last time I checked. Call a dealership for the part number and their cost, then go find it elsewhere (perhaps on www.gmpartsdirect.com) for less money. You might also be able to find one at a salvage yard for a LOT less money. I paid $100 for a compressor/drier/solenoid (the whole shebang) at Fierge Auto Parts in Quincy, Illinois. (www.fierge.com) You can do this yourself as well. It's a little tedious, but not too difficult for a do it yourselfer with basic tools. I'd give it a difficulty score of 4 on a 10 scale. Let me know if you want a description of how to do it.

The B1558 code I have no idea about. Maybe one of the electrical gurus can help with this one. Is it current or history?

Let us know what you find... Good luck!


01-04-05, 05:38 PM
Thanks alot M C, that was extremely helpful. Im sure i can knock out the o2 sensor, but could you tell me how to tackle the solenoid problem. I come to learn that alot of mechanics charge ridiculious prices to work on these cars and sometimes it wont be done right unless you do it yourself. As for the B1558 code, its current. My traction control seems to go off easily, im assuming thats related to the soleniod prob?

Once again thanks for your help.

01-07-05, 10:13 PM
OK, Eldo_Red, here you go:

To get at that solenoid, chock the front wheels, jack up the rear of the car and support it safely. Above the rear axle on the passenger side, you'll see some rubber grommets above a metal compressor cylinder and motor. Feel around up there and find the wiring harness coming out of the compressor assembly, then disconnect it. The compressor, solenoid, and air dryer are mounted on a bracket that attaches to the rear axle. There are 4 or 6 bolts holding that bracket on the axle, and they used several different brackets, so I can't tell you exactly where they are. On my car, the bracket kind of snaked its way around down by the wheel and it was a funny shape. The bolts should be fairly apparent. Just follow the bracket around until you find 4 or 6 of them. Now remove them. I think they're 10mm, and some of the spaces on my 96 SLS were too small for a 3/8" ratchet, so I would use a 1/4" if you can.

Once you get the bolts out of there, you have to carefully fish the compressor assembly out of its home, and it's nestled in there pretty well. There are some flexible plastic air hoses connected to the whole thing, so start by disconnecting those and laying them aside where they won't get water in them. There is a small metal clip holding the round plastic dryer assembly to the compressor body. On my car, I had to remove that clip and disconnect the dryer to weasel the compressor out of there. It'll take some patience, and it can also take as many as 5 Budweisers to do this. As your frustration level rises, I strongly suggest you avoid punching any sharp metal pieces in the general vicinity. On my car, those sharp metal pieces were designed to laugh at you and call you names as you lie there bleeding. It's another wonderful Cadillac innovation. (BBob, would you care to explain this?) Then, just as your head is about to explode with rage, the compressor will fall on it while you're not looking. While this might be absolutely hilarious if you were watching it on television, in this particular situation, it causes intense pain instead, which can only be relieved by a few more of those Budweisers and a little high volume swearing at your least favorite non-present relative or politician and his or her ancestors. This works best if you chain lots of vulgarities together into one humongous 53-syllable tirade. From what I've heard, mothers-in-law are frequent targets.

Now that you've skillfully removed the compressor, you should be able to find that solenoid pretty quickly. Air hoses go into it. If you take the cover off, it will probably be very rusty inside and clearly in need of replacement. Depending on what part you got to replace it, the reassembly and reinstallation procedure is pretty self-explanatory. Just replace whatever part you got and put it all back together. Putting the compressor back above the axle is not quite as frustrating as taking it out. If you can't remember how it came out, smashing the compressor into your forehead should remind you.

If you have to change over the bracket for the compressor, you might have to open up the crankcase. Be careful not to get any debris in there. Carefully wipe off the gasket and don't overtorque the bolts. Just close it up snugly and don't worry about it.

I've heard some people say it's wisest to replace the air lines going to the shocks when you replace the compressor because there could be water in the lines. That's not bad advice at all if you can take the time to do it. Otherwise, if they can be disconnected at the shocks, you might want to blow them out to make sure there's no water in the system to start with.

Once you get it all back together, air lines hooked up, wire harness reconnected, bracket bolts all tightened up, and stitches in your forehead, you'll be very disappointed when you get in the car and see that you still have the 1738 code. What the heck went wrong? Did that @*%hole MC give me bad advice? While that's not outside the realm of possibility, in this case you're still getting the code because you have to remember to change the fuse! On my 96 SLS, it was on the panel in the trunk, behind that fancy carpeted thingee covering up the back of the seats. The fuse is labeled either ELC or ALC. Replace the fuse with the same rating and you should be back in business with a 1738 code in HISTORY and a fully-functioning electronic level control system. It will ride better!

Let me know how it goes. I'll do what I can to help, but you're going to have to get your own beer, sorry.

Good luck!


01-08-05, 12:56 AM
Thanks alot M C, i hope changin the soleniod is as entertaining as your post, your gonna turn me into an alkey haha. Im gone try to tackle that task soon, i'll be sure to keep you posted. Thanks a million.

On another note, i changed the o2 sensor and passed the emissions but while driving home today i got this error message

P1153 - Heated Oxygen Sensor (HO2S) Insufficient Switching Bank 2 Sensor 1

Thanks again, have a great day

01-08-05, 10:32 AM
Sure enough, that's what the code means. Bank 2 sensor 1 is the sensor in the manifold for the front bank of cylinders. It's also changed out fairly easily by jacking up and safely supporting the front of the car and looking just behind and above the radiator support toward the driver side of the car. Same procedure. Use the O2 sensor socket you already bought or borrowed. Disconnect the harness, unscrew the sucker, screw the new one in there, reconnect the harness, ensure the wiring is routed properly so as not to come into contact with the manifold (using whatever clips may be provided for such purpose), done! I think the Bosch part number for the front sensors is 13-474. AutoZone carries it around here for $65, and you can borrow the socket from them for a fully-refundable $15 deposit.

Sounds like the sensors are giving out on you. Sometimes they all go out about the same time, sometimes one fails and they're all fine for another 20k miles. They aren't bad, O2 sensors are a normal maintenance part. They don't last forever and weren't designed to, so it's not like you got a lemon or anything. It happens.

Anyway, that should fix you right up. Let me know how it goes.