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Discussion Starter #1 (Edited)
OKay,

I made the paperclip jumper to bridge across the ABS diasnostic plug that's located in the area between the coolant reservoir and the ABS accumulator tank on my 1990 SPG. I got all 3 wheel sensor missing codes and the 1114 RF inlet valve code. I removed and cleaned all the sensors, blew out the holes with compressed air while spinning the rotor, and cleaned all the connectors to the wheel sensors and the main connector on the ABS distribution block. I cleared all the codes and test drove the car. Everything worked great and the anti-lock light only illuminated normally during initialization and went out as it should.

However, if I drive the car long enough to get it hot, shut it off, and then restart the 1241 error code returns (signal from RF wheel sensor is missing). I've checked and rechecked the wires and electrial connections to the RF sensor, with no visible problems in any of those components.

I've been messng with this problem for over a week and there's a definite pattern / predictablility to it. The error code never appears when the car is cold. It never appears while driving. It only appears on subsequent restarts after the car has been driven long enough to warm it up, shut off, and restart again. Occasionally I'll restart 3-4 times without a problem, but just when I think I have it fixed it throws the 1241 code again.

My inclination is to visit the 91 900 I know at the local Pick 'N Pull and get the RF sensor off of it. Unless someone on this forum can point me another direction.

Steve
 

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Did you correctly refit the wheel sensors? When new the sensors have a fibre pad on their face which is supposed to touch the tooth wheel on the CV joint. This sets the correct spacing for the sensor. Once the car moves, the pad gets worn away so you cannot easily re set the spacing...
 

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Steve Corgan said:
My inclination is to visit the 91 900 I know at the local Pick 'N Pull and get the RF sensor off of it.
Something's heat-soaking enough to cause the ECU to lose that signal. I'd be surprised if the heat from the brake is sufficient, which'd suggest that heat could be affecting the signal processing for that sensor in the ECU.

Mine's non-ABS, so I'm extrapolating slightly - where is the ECU? With the master, or inside the car?

I think I'd be tempted to troubleshoot a little more before replacing the sensor - can you swap LF and RF over? If so, do that, and see whether the fault moves with the sensor or stays.
 

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Discussion Starter #4
I was careful in refitting sensors. I read about the fiber washer in Bentley's but there was no sign of a fiber washer any where on my sensor. Since Bentley talks about taking the sensor apart on the benceh, I figured it must be inside the sensor. Each sensor did have a plastic sleeve that it slipped into.

A fiber washer on the end of the sensor that touches the wheel sending unit couldn't determine the gap that way. The sensor bolts tighten down against the casting in the steering knuckle. I think that fiber spacing washer must be inside the sensor.

Sc
 

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Discussion Starter #5
TooMany2cvs said:
Something's heat-soaking enough to cause the ECU to lose that signal. I'd be surprised if the heat from the brake is sufficient, which'd suggest that heat could be affecting the signal processing for that sensor in the ECU.
I'm thinking that it's definitely heat related. Why don't you think that the heat from the brake would be enough? There's a lot of heat coming off the brakes, second only perhaps to the exhaust system as a source of ambient heat.

The idea of swapping in a known good sensor sounds good. I haven't checked yet but I think the two front sensors may be swappable. But it maybe be a major job to get to the LF sensor wiring with the master cylinder and coolant reservoir crammed into the area where the wiring passes.

Bentley's does talk about disassembling the sensor so I might try that. Anybody know what to look for once I get it open, or if that's even a good idea or not? Bentley doesn't say much except a warning about that fiber washer.

A sensor from the Pick 'N Pull I'm sure will only be a few bucks, and the RF sensor that I need is an easy in and out. I could do that first. I might just get lucky.

Thanks for the help. Any and all is welcome.

Sc
 

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Discussion Starter #6
- where is the ECU? With the master, or inside the car?

I think that the ECU on my 90 SPG is under the back seat. At least there's some brake related component there. I loosened the large plug on it, inspected, cleaned it with electrical contact cleaner, and reseated it. Is that the ECU? IF not what is it and where is my ECU? I've read that the ECU is behind the pasenger side right kick panel, but I didn't check since I thought that I'd found it under the seat. Please clarify for me.

Sc
 

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Steve Corgan said:
I'm thinking that it's definitely heat related. Why don't you think that the heat from the brake would be enough? There's a lot of heat coming off the brakes, second only perhaps to the exhaust system as a source of ambient heat.
There's also a lot of cooling air flowing around.

I know that when I'm spanner-wielding, it's very rare for me to grab something round the brakes (other, of course, than the actual disk) and yelp in pain. Underbonnet, however, it's very common...

As a rule of (slightly singed) thumb, I've always found it holds me in good stead.

A sensor from the Pick 'N Pull I'm sure will only be a few bucks, and the RF sensor that I need is an easy in and out. I could do that first. I might just get lucky.
Ah, in that case, just swap'n'hope...
 

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Discussion Starter #8
I love going to the self serve junk yard anyway. My wife is beginning to think I've got a girlfriend on the east side (of the Mississippi River), which happens to be where all the nudie bars are in the St.L. area are also. The only stripping going on around me though are the Classic 900s.

What about opening up the RF sensor I have? Is there anything I can fix in there? Is it easily damaged? I'd hate to break it in case it's not actually the faulty component. Anybody know?

Sc
 

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Don't bother trying to open up the sensor because there's nothing in there except a permanent magnet and a load of wire and it's basically wrecked as soon as it's opened. If you've got a digital multimeter handy measure the resistance of the sensor across its terminals and compare it to the figures in the service guide (sorry I've not got the specs to hand but the figures are usually given at 20 deg. C). As the temperature rises the resistance of the sensor will change and this may well be the cause of the problem.


It's also worth comparing the resistance of the sensor at the sensor plug with the resistance at the multi-plug at the ABS ECU. If this is the same (give or take a little bit) it rules out the wiring between the sensor and the ECU. If it's slightly different try cleaning contacts, if it's either a dead short or an open circuit look for a broken wire or connector.
 

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Discussion Starter #10
Great!

That sounds like the information I needed. I won't have time until the weekend to implement what you suggest, but I will post the outcome when I figure it out.

Thanks Jim!

Sc
 

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Discussion Starter #11
Cold weather - No more ABS fault code

Well wouldn't you know that winter finally came to Missouri and the ABS fault code hasn't returned since the arrival of the cold weather and my last post to this thread. In my mind this serves to further support the hypothesis that my right front sensor problem (code 1241) is heat related. Or the other posiblility is that in my persistent wiggling, cleaning, and checking of the ABS system connectors I fixed the problem. I guess I'll know if the problem returns when the weather warms up.

Anyone have any other theories?

I did have occasion to go to the local Pick N Pull for some other parts and so I got a RF wheel sensor off a 94 900 convertible for $5.00. I'll probably just swap out parts if / when the problem returns.

In any case, it's hard to diagnose / fix if it ain't broke.

Thanks everyone for the input and help.

Steve
 
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