SaabCentral Forums banner
21 - 40 of 88 Posts

·
Registered
Joined
·
57 Posts
Ya, can't add it if you can't talk to it. What else will make a UEC seem dead when it isn't? UEC communicates on I bus (single wire) so a bad connection or two can drop modules off the bus. No power would do the same. Beyond that the failures get dicier. Here's an I-bus diagram. OBD port goes to CIM which goes to UEC via MIU. Note that failure in H102-1 can disconnect both REC and UEC from I bus (EDIT: and a few other things).
View attachment 283138
Thanks for your help, I took the fusebox out and tested for continuity from obd pin 1 to B2 and to B3 on the B block connector under the fusebox, all good.
 

·
Registered
Joined
·
1,811 Posts
Let's back up. Does main relay (leftmost in small fuse box in front of battery) pull in when starting? Also, UEC +15 enable signal comes from ISM, and pulls in R11 (3rd large relay from cabin in center of UEC) when ignition is ON.
 

·
Registered
Joined
·
57 Posts
Let's back up. Does main relay (leftmost in small fuse box in front of battery) pull in when starting? I suspect not.
Here is the odd part, I have checked the power +15 to the Ecm from the ignition switch through R11 relay to fuse 4 and then to B3, Ecm then grounds B24 to main relay 229, relay pulls and sends power back to ECM at B1 and B17 all good. I connected a test light to position 87 on main relay and turned the ignition on and off to see if the relay was sending. I tested continuity from relay position 87 to B1 and B17 all good. I can only assume that the power to B1 and B17 is good from that test because if I take off the connector 608b, that would also stop the ground to the main relay. The Wis is unclear about +30 to the ECM, one diagram shows fuse 2 to pin 21 on 608b and the the diags say check pin 36 for +30, I have checked both, there is no wire in on 21 (608b)The only other odd thing is my check engine light is no longer working, in the beginning it would stay on even if the car started, now it doesn't even light up.
 

·
Registered
Joined
·
1,811 Posts
CEL comes from ECU to MIU directly via H24-2 and H102-1. Have you checked those connectors?
 

·
Registered
Joined
·
57 Posts
I have tried to avoid ripping things apart unless I can see a correlation in the circuits to the problem, and H24-6 (V6) would be such a case, from what I can see it looks to be intact but might need a closer examination. H102-1 looks clean. I can see how the CEL is grounded from a signal from B50 (608) through these connectors, but I can't see any correlation between these connectors and the UEC missing on bus, unless I am missing something? Thanks for looking at this,
 

·
Registered
Joined
·
1,811 Posts
The I bus also comes through 2 different pins on H102-1, so it was worth a look.
 

·
Registered
Joined
·
1,811 Posts
So at this point (correct me if any of this is wrong - info is pretty spread out)

Car does not turn over
The only DTC s of note are +15 UEC and UEC and REC missing from bus
UEC +30 and +15 test OK
I bus has continuity to UEC from OBD port via MIU
known good UEC also shows same faults
H102-1 has been tested, checked, and cleaned
 

·
Registered
Joined
·
57 Posts
I thought the I bus only went through that connector at pin8, so I did check for continuity between DLC pin1 and the B connector under the fusebox at pins 2&3 it looked good, continuity and no resistance, so I just assumed h102-1 must be a good connection.
 

·
Registered
Joined
·
1,811 Posts
OK, time to jumper the starter relay and see if car turns over. ECU was not previously mentioned, unless I missed it.

With ignition on, jumper pins 30 and 87 on starting relay (R8 in UEC). Does car turn over?

To verify, this car is B284 (6 cyl) with manual transmission, correct?
 

·
Registered
Joined
·
57 Posts
It's a V6 automatic convertible, jumping R8 will turn the car over, but not start. Let's go back to the beginning, I believe this is a ground problem, that's why I was asking about the wires on the ECM originally. The UEC which shows no voltage and is missing on the bus, is grounded at G30a G31 and G33s. I have checked at the body, the grounds seem ok, but I have only tested for continuity from G33s to B18 on the connector under the fusebox. I will check G30a to F27 and G31 to F26 tomorrow. The check engine light will only come on with a ground signal from B50 on the Ecm. The modules on the bus have their own grounds which might explain why no others are missing on the bus. Another anomaly is the fuel gauge doesn't always register, which again is grounded by the ECM from B25. The main relay 229, which I believe is working, but may not be as it should, is grounded from B24 on the ECM. There was a time when the car would start, but I always thought it was turning over slower than it should, even though the battery was brand new. So my thinking was; if the ECM and UEC shared some ground positions, maybe that was the source of the problem. I should add that I bought this car in this condition, believing that because of covid restrictions, it would be fun to fix it, now I'm ready to burn it.
 

·
Registered
Joined
·
1,811 Posts
but may not be as it should
Relay is either good or bad. You can test with clip leads and multimeter.

OK, so you know from WIS that ECU turns on starter relay R8 directly, and CEL directly. Neither are currently working.

Have you looked at the starting circuit for B284 auto trans? The permissive signal from TCM loops through UEC to ECU on pins M22 and M28 after coming through H10-2. This must be true to turn over car. It is the park switch.

The thing with these cars is that there are a number of multipin connectors (H24/H42 and H102-1 for example) that connect varied circuits. These can also degrade or fail and cause strange, seemingly unrelated symptoms, just like bad grounds.

I don't remember if you said you had measured battery voltage or said battery age. That's always the "Is it plugged in?" question with these cars.
 

·
Registered
Joined
·
57 Posts
The battery is new and has been load tested twice. I've studied these wiring diagrams for months, it's like looking into a bowl of spaghetti. I tried to follow the wires all over this car, it's a quagmire, and it is easy to get sidetracked. There has to be an explanation for Uec missing on bus, and there has to be an explanation for, UEC battery voltage *V, UEC ignition voltage +15 * transport fuse *, until I discover the reasons for those errors, I don't think I am going to solve this problem. Again thanks for your help
 

·
Registered
Joined
·
1,811 Posts
Yes. I'm thinking that might just be the problem. Needs to be confirmed with a few measurements, though. The ME9 ECUs don't fail very often.
 

·
Registered
Joined
·
1,811 Posts
The battery is new and has been load tested twice. I've studied these wiring diagrams for months, it's like looking into a bowl of spaghetti. I tried to follow the wires all over this car, it's a quagmire, and it is easy to get sidetracked. There has to be an explanation for Uec missing on bus, and there has to be an explanation for, UEC battery voltage *V, UEC ignition voltage +15 * transport fuse *, until I discover the reasons for those errors, I don't think I am going to solve this problem. Again thanks for your help
I thought you had verified that ISM is indeed switching on +15 through UEC?

If you have I bus continuity to UEC and it's not on the bus, either its bus transceiver is hung or something else is impairing the bus (like a failed transceiver on another module, or a crappy short to ground with a few ohms resistance). It is also possible the CPU in the UEC is not running, due to lack of +30 power.

If you have CEL continuity to the ECU, and the CEL doesn't light, you may have an ECU problem.

If you have no start relay AND you have park switch input true AND CIM/ISM/SCL are happy, you may have an ECU problem.
 

·
Registered
Joined
·
57 Posts
+30 through fuse 2 to B36 (ECM) = working, Ism +15 to B3 (ECM) = working, B24 (ECM) ground to main relay (229) or R4 = working, power from main relay position 87 to B1 and B17 (ECM) = working. +X signal to B58 (ECM) = working,
I was told by a Saab guy to ignore "ECM missing on bus" message unless it's the only thing missing. The reason being; a failure of the UEC will generate this fault message? This is the problem, conflicting information, if you use the WIS diag for; "one or more systems connected to P-bus missing", the UEC is not one of them, I wouldn't expect it to be, it's on the I-bus? But again, the P-bus wires come into the UEC from the ESP module, on connector B at 6 and 17, and go out again on the M connector at 1 and 30 to the H10-2 connector, through the TCM and back through H10-2 to the ECM. The Wis also lists the UEC as one of the components of the P-bus. So is the UEC missing on the I-bus or missing on the Pbus, I have no idea? The Wis is full of errors so it's hard to follow, as an example, +30 through fuse 2 to B36 on the ECM, Wis shows that wire as going to B21 in one place and B36 in another. I think the reported voltage problem, UEC battery voltage *V, UEC ignition voltage +15 *, transport fuse *, and the UEC missing on the bus, are the clues to what's wrong here. If I can answer those questions, and the bus question, I might be closer to solving this. Thanks for your patience.
 

·
Registered
Joined
·
599 Posts
Discussion Starter · #38 ·
you are a little deeper into this then i am. But i'm going throw something out there.
If UEC is missing, seems you have all the correct voltages, i would remove everything downsteam on the I-bus from the UEC. Meaning remove the wire from B2 on the UEC connector.
Sound like you already OHM'ed the wire from the MIU (7) thru connector H102-1 to UEC B3.

You already swapped the UEC from a working vehicle?

Lastly, if you are missing both the ECM and UEC (two different buses), the only component they have in common in the CIM (and maybe the ICM).
 

·
Registered
Joined
·
1,811 Posts
You have at least two things not working that are connected directly to the ECU: The CEL and the starter relay. It seems reasonable to find out why this is so.
 

·
Registered
Joined
·
599 Posts
Discussion Starter · #40 ·
You have at least two things not working that are connected directly to the ECU: The CEL and the starter relay. It seems reasonable to find out why this is so.
Tho not my car, i like to read and learn. Trying to understand if there is a bad/defected ECU, would that cause the UEC to be missing? Thinking it is two different Buses, one wouldn't effect the other. I'm sure i'm missing something, so i'm asking.

If you don't have a UEC, you wouldn't crack?
 
21 - 40 of 88 Posts
Top