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Discussion Starter · #1 ·
Hi,

I retrofitted a B5.5 FIS cluster (3B0 920 847) to my 2000 B5 Passat which originally contained an MFA cluster (3B0 920 922).

I have changed the EEPROM of the new cluster to that of an MPH (3B0 920 947) and I have done the necessary soft coding and key matching. The cluster works fine however there is an error in VAGCOM relating to an intermittent fault with the outside air temperature sensor (once I get back to the car I will get the exact error code to post). After reading up about this it seems like a common occurrence when retrofitting a B5.5 cluster in a B5, the assumption is there are perhaps differences in the way the clusters retrieve the outside air temperature, however I am confused as to what I should do.

My original cluster displays the outside air temperature without a problem, indicating I must have the sensor fitted I assume?
So what is the issue then, does the new cluster retrieve the sensor information from a different pin on the T32/A connectors than the original?
Does someone have a pinout at least for the T32 connectors of both a B5 and B5.5?

Thanks,
James
 

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Seems like you're on the right track, as VWs have used the same ambient temperature sensor since the MFA first appeared in the US 1986 Scirocco 16Vs.

Probably just a matter of moving one or two wire terminals in the T32 to have a functional amb. temp. readout.
 

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Discussion Starter · #5 · (Edited)
Seems like you're on the right track, as VWs have used the same ambient temperature sensor since the MFA first appeared in the US 1986 Scirocco 16Vs.

Probably just a matter of moving one or two wire terminals in the T32 to have a functional amb. temp. readout.
I actually saw a post whereby someone determined the part numbers of the OAT sensor for the car from which their FIS cluster came from, and the car to which they retrofitted it, differed... so perhaps there are different versions. Here's the link (second post):

http://www.ukpassats.co.uk/phpbb/viewtopic.php?f=8&t=3780&start=0&st=0&sk=t&sd=a

Any chance someone can confirm this by checking for me? I would have thought it would just be a simple three wire sensor and so even if the part numbers were different it would communicate with the ECU in exactly the same way...

But yeah my immediate thought was different pin assignments.

do you happen to know the year-model b5.5 the full fis came from? it could just be an incompatible part.... maybe.
It was a 2002 model. I remember clearly because I was glad about it, as I didn't check the IMMO version when I ordered but luckily it turned out that 2002 is IMMO 3 (so I was able to do the tweaks to the FIS and needles :D).

There you go! Forget the sections I highlighted, these pictures were posted by me a couple of months ago when fighting against the CAN bus :(
Thanks for the images, it appears the OAT sensor is on pin 26 on both so there's no issues there. And anyway both my original cluster and the retrofitted FIS cluster are in the 05-99 model range :/
 

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I actually saw a post whereby someone determined the part numbers of the OAT sensor for the car from which their FIS cluster came from, and the car to which they retrofitted it, differed... so perhaps there are different versions. Here's the link (second post):

UKpassats.co.uk ? View topic - Just for the hell of it...flash b5.5 cluster eeprom onto b5

Any chance someone can confirm this by checking for me? I would have thought it would just be a simple three wire sensor and so even if the part numbers were different it would communicate with the ECU in exactly the same way...

But yeah my immediate thought was different pin assignments.



It was a 2002 model. I remember clearly because I was glad about it, as I didn't check the IMMO version when I ordered but luckily it turned out that 2002 is IMMO 3 (so I was able to do the tweaks to the FIS and needles :D).



Thanks for the images, it appears the OAT sensor is on pin 26 on both so there's no issues there. And anyway both my original cluster and the retrofitted FIS cluster are in the 05-99 model range :/
Can't get into that forum as i'm not registered.

Here goes both screenshots from the '98 and from the '02:




Considering the applications listed on ETKA it looks like the 8Z0 is the correct sensor for later models:

 

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Discussion Starter · #7 ·
@VitorBart Thanks for those, that's really helpful! So do you think there is a difference in the sensors considering the different part numbers? I mean they are such simple devices I would have assumed the older sensor would still work with the newer cluster...

I'm considering buying the newer sensor and fitting it to see what happens, I assume the connector and look are the same anyway. I'm just reluctant to keep throwing money at things to just "try" and hope it works that's all.
 

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Discussion Starter · #8 · (Edited)
Also, as many people have retrofitted b5.5 clusters to their b5s, I would have thought there would be many people who faced the same error as me. I was kind of hoping they would see this thread and could tell me how they solved it. If they didn't face the same error then that suggests perhaps the original sensor does work with the new cluster and my issue is somewhere else...
 

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Also, as many people have retrofitted b5.5 clusters to their b5s, I would have thought there would be many people who faced the same error as me. I was kind of hoping they would see this thread and could tell me how they solved it. If they didn't face the same error then that suggests perhaps the original sensor does work with the new cluster and my issue is somewhere else...
That makes perfect sense to me, I really can't tell you if they are the same part or not, though. :(
 

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In this case, the two sensors may be different only because they pair with clusters that use a different range of resistance to map to a temp range. Without having access to the specs it will be hard to know if they are compatible.

One way might be to look at the FSM/ELSA for a B5 and the FSM for one of the cars that takes a FIS. There is typically a graph of resistance v. Temp given for these types of sensors to help you test if they are defective and need to be replaced. compare the two graphs and you'll know right away if they are compatible. If you are lucky it might be only a matter if adding a small resistor to bring the B5 sensor within the range the FIS cluster expects (what are the chances thought).

Maybe someone here with access to Elsa can check those and post back.
 

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Discussion Starter · #11 · (Edited)
In this case, the two sensors may be different only because they pair with clusters that use a different range of resistance to map to a temp range. Without having access to the specs it will be hard to know if they are compatible.

One way might be to look at the FSM/ELSA for a B5 and the FSM for one of the cars that takes a FIS. There is typically a graph of resistance v. Temp given for these types of sensors to help you test if they are defective and need to be replaced. compare the two graphs and you'll know right away if they are compatible. If you are lucky it might be only a matter if adding a small resistor to bring the B5 sensor within the range the FIS cluster expects (what are the chances thought).

Maybe someone here with access to Elsa can check those and post back.
That seems reasonable, however I would have still expected the sensor to work even if it provided the incorrect reading.

It appears that both sensors are the 3 wire type (maybe I'm wrong), so they would both have power, ground and signal wires. Even if the wires were in a different order it would just mean the cluster may see the +12v or 0V as the signal instead of the correct reading. So I would still expect the cluster to output an incorrect reading...

But as you say, if someone can confirm for sure the wiring for the two variations of sensor (8D0 820 535 and 8Z0 820 535) and the pinouts on the connector to the sensor, then I can confirm this theory. I'm more inclined to believe the wiring to the back of the cluster is slightly different, but the pinouts provided by VitorBart suggest they are the same. I wonder if theres an additional connection from the OAT sensor, for the B5.5 cluster, which goes to the blue connector maybe?

EDIT: it appears both sensors are cross-compatible, the difference being that the 8Z0 has the connector for the harness at the back of the sensor whereas the 8D0 has some wire off the back of the sensor and then the connector. See: http://forums.quattroworld.com/s4/threads/4100.phtml
 

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Discussion Starter · #12 · (Edited)
There is another interesting link in which the guy did the exact same swap as me (B5 MFA to B5.5 FIS) and encountered the same problem (the OAT worked fine on the B5 MFA but in the B5.5 FIS gave an error in VAGCOM and no reading). He worked out that if you wire the sensor directly to pin 26 on T32b then the sensor works on the B5.5 FIS cluster. This is strange that the cluster doesn't like the stock wiring of the sensor and requires it to be wired directly to the cluster, I wonder how the stock wiring is routed? I still feel that although this may be a solution to the problem, there must be another way that does not require re-wiring directly to the cluster...

link: http://forums.tdiclub.com/showthread.php?t=288148
 

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it has to do with the differences in the cluster. by having a full FIS on it, that means it's a different board, and thus completely different unit inside and out. needing to change pin-outs is not uncommon in those scenarios. sounds like we nailed it! :)
 

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Discussion Starter · #14 ·
it has to do with the differences in the cluster. by having a full FIS on it, that means it's a different board, and thus completely different unit inside and out. needing to change pin-outs is not uncommon in those scenarios. sounds like we nailed it! :)
That's true, except the diagrams provided by VitorBart, and the information in the links I provided, shows the pinouts are the same between the different boards (OAT sensor to T32b pin 26).

The only solution I have found is to wire the sensor directly to this pin as opposed to going through the stock harness. Which is strange because I don't understand why this would make a difference (the sensor is the same, the pin connection is the same, the only difference is the wire from the sensor to the cluster would be perhaps shorter)... As this is a common retrofit, I'm hoping someone that has done it may be able to at least confirm whether they have experienced the same problem as me?
 

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well, on those models that had the full fis cluster, it could literally have been a wire directly form the cluster to the sensor, through the harness.

remember, things always get weird when you retrofit!
 

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That's true, except the diagrams provided by VitorBart, and the information in the links I provided, shows the pinouts are the same between the different boards (OAT sensor to T32b pin 26).

The only solution I have found is to wire the sensor directly to this pin as opposed to going through the stock harness. Which is strange because I don't understand why this would make a difference (the sensor is the same, the pin connection is the same, the only difference is the wire from the sensor to the cluster would be perhaps shorter)... As this is a common retrofit, I'm hoping someone that has done it may be able to at least confirm whether they have experienced the same problem as me?
So... let me get this straight. The solution simply bypasses the harness, and wires the sensor output wire directly to the back of the cluster (Pin 26)?


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Discussion Starter · #17 ·
well, on those models that had the full fis cluster, it could literally have been a wire directly form the cluster to the sensor, through the harness.

remember, things always get weird when you retrofit!
But the thing is, that's the same on the B5, sensor through the harness to the cluster. The solution I linked to suggests to remove the harness and wire sensor to cluster, which doesn't make any sense to me in terms of why it would make a difference...

So... let me get this straight. The solution simply bypasses the harness, and wires the sensor output wire directly to the back of the cluster (Pin 26)?


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Yes apparently so, I haven't tried (yet) as it seems stupid to me too... I'm more inclined to believe it was some other factor which caused this to work for the person who suggested it, but they thought it was this as perhaps they also wired directly at the same time...
 

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that was my thought as well. i would expect the cluster circuit would have some build-in tolerance for a possibly slightly longer or shorter harness length, if that is all that is going on here. I am pretty sure the thermistor that is the guts of the OAT sensor would be putting out resistance values at least an order of magnitude higher than any possible resistance variation that could come from various wiring harnesses.

jrelder, to clarify, are you saying that the wiring diagrams for your car show that the wiring harness for the OAT directly connects to the proper pin on the cluster but that it only shows the correct temp when you wire it using your own wires? That would indicate at a minimum that the wiring diagram is not correct.
 

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But the thing is, that's the same on the B5, sensor through the harness to the cluster. The solution I linked to suggests to remove the harness and wire sensor to cluster, which doesn't make any sense to me in terms of why it would make a difference...
if you know for fact that the sensor's wires do NOT go through any other modules, you could pull and repin the connector for those two wires without need to overlay a new wire for it.

however, as i said, these are two different cars! you can ask PZ about how different pretty-much everything, wiring and ALL was with his v6 to 1.8t swap ;)
(hint: he's still figuring it out in situ)
 

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Yes apparently so, I haven't tried (yet) as it seems stupid to me too... I'm more inclined to believe it was some other factor which caused this to work for the person who suggested it, but they thought it was this as perhaps they also wired directly at the same time...
that was my thought as well. i would expect the cluster circuit would have some build-in tolerance for a possibly slightly longer or shorter harness length, if that is all that is going on here. I am pretty sure the thermistor that is the guts of the OAT sensor would be putting out resistance values at least an order of magnitude higher than any possible resistance variation that could come from various wiring harnesses.
Yeah, i'm also mystified by this solution/explanation. I would also expect that the sensor output would be an order of magnitude different than the slight (possibly immeasurable) difference in resistance caused by a harness or wire length difference. We must be missing something else here.

I've got my car in service position right now, and have been getting intermittent faults from the OAT sensor. If i remember and have enough time i might pull it off and bench test it to see what resistance levels the sensor actually outputs with temp variation, since i should really look into whats causing the connection faults anyway...


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