ABS Module Trifecta + Limp Mode + P1746- Which To Tackle First??

[RustE34]

Hello all- Been a while since I've been on here. At any rate, picked up a 200k mile 2001 530i for a song, and just working out some issues with it, and have come to a head.

Vehicle has gotten a cooling system overhaul last week. Now that thats up to par- I am dealing with the trifecta ABS lights, inop speedo, the normal song and dance for a bad ABS module. I read that you can disconnect the module and it will drive just fine, or isolate certain leads to regain speedo etc.

The issue I am having is the car goes into "limp mode" (nothing displays on the dash readout) and will not rev past 2500 rpm. I got the codes read, and first time around got p0500 (speed sensor) p1746 (transmission solenoid <9v condition). The codes were cleared, and the car drove normally for about 1/2 mile, then "Service engine soon" light back on, back into limp mode, so I turned around and got the fresh codes read again. This time we had p0500, p1746 and a new p0734.

My question is- Could an abs module failure cause the transmission related codes as well? shouldn't the vehicle operate normally (not in limp) with the module disconnected? Or do I have a few seperate issues here (Trans solenoid wiring, potential low fluid etc)

Which would you tackle first? I am into this car very little money, and would rather exhaust inexpensive diagnostic avenues first before replacing and recoding a new ABS module.

Thanks in advance.

[toybreaker]

get the BMW specific codes read and report back.... OBD codes tell you d!ck on a bmw...

[StRaNgEdAyS]

Also verify your voltage at the battery while the engine is running

Sent from my G8141 using Tapatalk

[RustE34]

New Battery but will triple check running voltage. Would low fluid cause an apparant limp mode, but no "Failsafe" being displayed?

[Ed CT]

You may want to check the speed sensors at the front & rear wheels (forget which sides they're on). The wires and connectors do crack and short/break. That would explain the speedo. I think the slushboxes include wheel speed into their equation, too.

[edjack]

There are two speed sensors inside the trans, too.

[1823alex]

The bad speedo is likely a bad wheel speed sensor or ABS module. I've also seen a thread stating that one of the wheel speed sensors is also responsible for how the transmission shifts - however I don't know how the transmission would work without it.

[rbelton]

First you will need a scanner capable of accessing the ABS codes. Pull the ABS code(s) first to diagnose the issue.

ABS module rebuild is only $90 or so, wheel sensor is not expensive either. But scan first to give you the right direction to go in.

[geargrinder]

Yeah thing to know about trifecta and reading the ABS/DSC codes is....

If its a wheel sensor(s) only then you'll generally reliably get a code for the wheel sensor(s). Clear it, comes back, clear it, comes back exactly the same in exactly the same time frame.

If the actual module board is failing, then you might get phantom sensor codes (because the board connections to sensors are intermittent), and you might even get no codes, because the whole module is just crapping out intermittently. If its the board then the codes - if any at all - will sometimes be more erratic in what and when they show up.

Summarizing - my rule of thumb is: if a guy has 1 or 2 sensor errors and they are consistent always, then go for sensors first. If its sporadic, inconsistent, and especially if sometimes no codes even appear... then its prob the module - which is a notorious bad guy with age.

BBA-Reman is your place for repairing the module. There are plenty of bad stories of guys using cheapo alternatives that crap out in short order, so if you go elsewhere, choose carefully or be prepared...

Re: the trans, I would look first at the wiring/connectors to the slushbox itself. As mentioned, the generic pee-pee codes leave a lot to be desired. Also as mentioned is that an internal speed sensor or is it the wheel speed signal?
But given that there's 2 codes (at least, a true BMW scanner might show some others...), I'd be more inclined to generally look for wiring / connection problem than to believe that 2 different things are broken.

[RustE34]

Okay so update- I brought the vehicle to a local foreign auto shop, with "A reader to read each module individually as needed" for a more accurate diagnosis/ codes etc. After spending the morning with it he calls back to say "Bad news, for some reason I cannot communicate with most any module except for 1 or 2, and am getting nothing from the ABS module. I don't want to throw parts at it so I am sorry I cannot figure it out" He then suggested Ken Baker Auto (dealership prices) or the Dealership itself.

Before bringing it in, I attempted to test the ABS sensors with my Diode setting of my DMM, with no luck at all. All came back Open line with no voltage reading, in both anode and cathode directions. I could just suck at that test, because it is unlikely all 4 ABS sensors are bad. I bought this car non running, so I have no previous history of issues.

Where to next? Don't want to give up on this party animal just yet. Should I replace all 4 speed sensors and abs module? What about the p1746?

I drove the car to this shop about 3 miles, and it cruises nice, wont go above 2500 rpm, and every so often I feel a slight "hiccup" in the trans. It is just a quick half a second miss it feels like.

Any input is appreciated.

[RustE34]

Is there a chance that other modules were shorted out somehow? Anyone want to buy a nice clean 530i lol.

[1823alex]

I doubt other modules were shorted out, but maybe.

Haha I'll buy parts off of your 530 for my 530, is it black sapphire metallic with a sand / beige interior?

This is just my opinion, but I prefer to read the modules myself to confirm the issue. It's possible the person didn't know exactly what they were doing, messed up or got confused etc.

I'd just get the PASoft BMW Scanner 1.4 for like $15 - 30 on Amazon and use that to read the codes - If you keep the car you'll definitely need it often. I keep mine in my car lol.

[geargrinder]

Is there a chance that other modules were shorted out somehow? Anyone want to buy a nice clean 530i lol.

Yes, there's very much a scenario where one module in the car craps it, then 'takes down the bus' so none of the rest of the modules can communicate. Look below.

Notice the DME and transmission module (this says AGS but an "EGS" is what technically your car has...) are on one diagnostic line, while the ABS/DSC and cluster are on a different diagnostic line.

Ignore the 20-pin, that was discontinued in 2000. The pins on the OBD you're concerned with are 7&8. And #8 is the one that has the ABS/DSC and cluster on it. The stuff that ain't workin'.

NOW, some cables / software aren't wired up to check pin 8.

So if the guy you went to doesn't REALLY have BMW compatible crap, then his gear won't be checking that pin. "Local foreign auto" doesn't mean dickpoop in general, except that the guy owns metric sockets. You gotta have the right gear to scan these cars. Hell I can do almost anything on a BMW but coudln't even start to begin on a Volvo, this stuff requires either make-specific gear, or, really $$$ stuff that is truly customized for each brand. Even the Snap-On 'all brands' diagnostic gear really kinda sucks for brand-specific tasks half the time. Anyway...

FIRST thing in fact is to check if you've got / he has / whoever-has... gear that looks on pin 7 & 8... If its not real BMW compatible then everything is probably fine but the gear is wrong. If you have a proven BMW-compatible setup (i.e. can scan other cars and see ABS/cluster/everything else) then... move on...

Next thing I'd check is if the OBD connector looks OK around pin 8. Is there a wire to it, etc. 7 & 8 are both "K line" terminals meaning that if nothing is talking they should 'sit high', aka you should see voltage on them if nothing is talking. Do you see battery voltage on both 7 & 8 with ignition turned on but otherwise nothing going on?

Depending on answer to that, you can look deeper. If 8 is 0V, then could be wiring or could a bad module be taking down the bus? Disconnect the ABS and see if you can scan the cluster. If so, then its a bad ABS module (or a shorted ABS connector). If not, disconnect the cluster and try the same. The "LEW" is the steering angle sensor, bit of a PITA to disconnect that but its' theoretically also a possibility.

Now, in pure wiring terms, terminal 8 goes to a splice in the drivers footwell, and all the wires are white-with-violet-stripe. If you peel back carpet and find that, you can test and disconnect one wire at a time and see if and when the voltage disappears (another way to accomplish the previous without going to the individual modules).

Ima gonna bet "Steve's Got Metric Sockets Foreign Auto" doesn't really have the right cable and his stuff doesn't look at pin 8. But maybe there is still a problem w/ the car.... if so do the above...