Saab ECU Communication Problem

[johnsmith222]

Hello,

Car: Saab 9-3 1.9TiD Z19 DTH Engine Saloon - 2007 model full facelift (interior and exterior).
ECU: Bosch EDC16 ECU

I am having a problem with my car, and it specifically relates to the ECU. I have a fair bit of experience with these cars, but I've had an electrical fault that started a few weeks ago which have rendered the car undrivable.

The fault:

Car will not crank OR will crank intermittently for very short bursts. Very occasionally it would crank properly.

The code:

U2105-00 . This code is a can bus communication error. The code shows up in the ABS/TCS module, AND the steering module. I do not believe these modules to be at fault. The fault seems to be the ECU. This is supported by no communication with the ECU using OPCOM.

Troubleshooting:

Please note, I have a good high quality VARTA battery that is 1 year old, tested with a dedicated battery charger and charged. I have also cleaned the battery terminals, grounding points for the ECU (noted as G2, under the battery tray).

The ECU is the Bosch EDC16 ECU.

This ECU has 2x permanent live pins. Pins 1 and 5. Both these pins have good stable voltage 12.6V. The resistance between the fusebox (UEC) and pins is good.

The ECU also has a switched live at pin 28. This pin has good stable voltage, and good resistance between the ECU connector and fusebox.

There are 3x ground wires. Pins 2, 4 and 6. All 3 of these pins have a good stable ground with low resistance to the grounding point.

I have bypassed the ECU relay by bridging the 30 and 87 with a wire to eliminate the wiring which powers the ECU. This is a single wire that goes between the 30 of the ECU relay, and pin 72 of the ECU.

I have checked the can bus pins 83 and 84 to see if they have continuity between the fuse box. Each pin has good continuity/low resistance.

I have checked resistance across these two pins. It shows 120ohms when the ECU connector is disconnected (normal).

Finally, I have checked the can bus resistance at the OBD2 port across pins 6 and 14. This shows the expected 60 ohms (63 ohms but near enough).

Does this sound like the ECU itself is likely to be at fault, or am I missing something? I'm preparing to send it away and pay for it to be tested/possibly repaired, but the intermittent fault is throwing me off. Surely if it was the ECU it would be consistently dead?

Thank you!

[E-bmw]

Aside of the can-bus issues for the moment.

You do not mention battery/engine /chassis earth connections, these could cause the non-cranking issue.

What is the battery voltage showing when you are trying/cranking the engine? As in, does it drop off significantly?

I know you think the battery is good but have you tried to start it with a booster pack/second car or battery connected?

Back to the can-bus error.

What are you trying to connect to the vehicle?

Can you get hold of another reader to try?

[Dynion Araf Uchaf]

You probably need to watch this guy disgnose a similar problem on a saab

It’s a 3 parter.

But here’s part 1

https://youtu.be/MVz6j2A8eFQ?si=a2HBry7G0Q6sl-8f

[LordLoveLength]

Do have a check engine light when it’s playing up? If not, do you then have power where you expect it?
If the ecu isn’t powering up properly it won’t turn the check engine light on.

Have you got a scope to look at the canbus signals? There could be absolute rubbish on there from another module.
Although your canbus resistance seems ok, have you measured each leg to ground? Could be an issue there.

Column Interface Modules are notorious for problems. Horn and indicators working when it’s playing up?

[johnsmith222]

E-bmw said:

Aside of the can-bus issues for the moment.

You do not mention battery/engine /chassis earth connections, these could cause the non-cranking issue.

What is the battery voltage showing when you are trying/cranking the engine? As in, does it drop off significantly?

I know you think the battery is good but have you tried to start it with a booster pack/second car or battery connected?

Back to the can-bus error.

What are you trying to connect to the vehicle?

Can you get hold of another reader to try?

Thanks E-bmw. I've not had a chance to check the voltage when it does decide to crank as it's so intermittent, but it cranks strongly on the odd very lucky occasion, but most attempts there is 0 crank, or it will crank for a fraction of a second at a time.

I've not tried with two batteries connected but Ive swapped for another known good battery which I have spare (saved from another saab 9-3 after a friend crashed).

I have:

1. Cleaned up the battery posts on both batteries so they look in "better" (shinier) condition than brand new.
2. Cleaned the inside of each battery terminal
3. Removed the negative lead from the gearbox, and a second grounding point under the battery tray (there's only 2 connections) and cleaned them
4. Cleaned the additional leads attached to the positive terminal and cleaned these too.
5. Cleaned the positive lead that goes into the fusebox.
6. Replaced the fusebox ("underhood electrical centre").

This could still be a ground issue though, and it's odd that it's intermittent.

In terms of the computer, I'm connecting a laptop with the "OPCOM" software installed on it, with a specific OBD2 to USB reader. I've used this for the past 10 years without issue. It can communicate with each car module seperately including reading fault codes. It can read fault codes in every single module apart from the ECU, which can only happen if the ECU is dead, doesn't have power, or doesn't have communication.

The U2105-00 code is present in the TCS/ABS module, and the steering unit (seperate modules). The fault in these modules along with the inability to communicate with the ECU definitely shows that the ECU/power/communication/ground to the ECU is at fault.

Dynion Araf Uchaf said:

You probably need to watch this guy disgnose a similar problem on a saab

It s a 3 parter.

But here s part 1

https://youtu.be/MVz6j2A8eFQ?si=a2HBry7G0Q6sl-8f

Thank you Dynion. I haven't seen that video so I'll work my way through it and see if it gives me any ideas what the issue could be. Hopefully it gives some ideas

You could well be right. Maybe there is still a ground issue so it's worth investigating to see if it could be. I've measured resistance to the ECU grounding point, but still need to measure resistance from the ECU grounding point and negative post. Thanks.

LordLoveLength said:

Do have a check engine light when it s playing up? If not, do you then have power where you expect it?
If the ecu isn t powering up properly it won t turn the check engine light on.

Have you got a scope to look at the canbus signals? There could be absolute rubbish on there from another module.
Although your canbus resistance seems ok, have you measured each leg to ground? Could be an issue there.

Column Interface Modules are notorious for problems. Horn and indicators working when it s playing up?

I intermittently have a check engine light when it is playing up. It sometimes flickers on and off, sometimes I have no check engine light, and sometimes it is on for short times. I interpret this as if the ECU has a poor connection. It's rapidly randomly going on and off. The fuel pump will cycle. then stop. Then cycle. This makes me think that even though I have measured the important power and ground pins, maybe there is something that is very intermittent poor connection. Maybe it reads like it's good but when the ECU is demanding it, then it's insufficient (e.g. bad connection). Times when the engine light has co-incided with the engine cranking.

Unfortunately I don't have a scope so wouldn't be able to see the canbus signals, but might need to see if it's worth getting one.

I've not measaured each leg to ground, but can do and see if there is an issue.

The indicator seemed fine as I accidently hit it on, but that's something else I can test for to see if the issue could be there. Thanks.

Edited by johnsmith222 on Monday 10th November 20:41

[E-bmw]

Just a point to note, which you likely have already realised.

You may well have 2 actual problems here hence why I split my reply in 2 earlier.

The "intermittent" cranking/CEL could be one issue that may/may not be related to the ECU comms issue.

You ask if the intermittent nature of the cranking bit makes any sense. It could if you have a wiring issue that is either a connection or a wire not passing current all of the time.

Unfortunately, I use the words could & may extensively above as due to the intermittent nature of your issues faults like this can be VERY hard to find. Often IF it is a wiring/connection issue a wiggle/tug test can be helpful to find the area of concern. I stress the IF there, sorry I can't be more specific obviously.

Good luck & keep us informed.

[johnsmith222]

E-bmw said:

Just a point to note, which you likely have already realised.

You may well have 2 actual problems here hence why I split my reply in 2 earlier.

The "intermittent" cranking/CEL could be one issue that may/may not be related to the ECU comms issue.

You ask if the intermittent nature of the cranking bit makes any sense. It could if you have a wiring issue that is either a connection or a wire not passing current all of the time.

Unfortunately, I use the words could & may extensively above as due to the intermittent nature of your issues faults like this can be VERY hard to find. Often IF it is a wiring/connection issue a wiggle/tug test can be helpful to find the area of concern. I stress the IF there, sorry I can't be more specific obviously.

Good luck & keep us informed.

Apologies for the delay in responding. I had a run of bad luck when it comes to transport with:

1. The car ECU problem.
2. My commuter motorbike developing an electrical problem at the same time.
3. Having to cycle into work, and my 5 day old tyre getting punctured with a big cut in it.

Thankfully I’ve fixed problems 2 and 3 so I’ve returned to the car fault.

I sent the ECU away for testing by ECUtesting. I am convinced that the problem was either a wiring issue, or a dying/dead ECU. They have tested the ECU and have confirmed that it is working fine on the bench, but offered a rebuild just in case. I have declined the rebuild as I just wanted the testing to confirm the ECU works before I start replacing wires.

E-bmw said:

Just a point to note, which you likely have already realised.

You may well have 2 actual problems here hence why I split my reply in 2 earlier.

The "intermittent" cranking/CEL could be one issue that may/may not be related to the ECU comms issue.

You ask if the intermittent nature of the cranking bit makes any sense. It could if you have a wiring issue that is either a connection or a wire not passing current all of the time.

Unfortunately, I use the words could & may extensively above as due to the intermittent nature of your issues faults like this can be VERY hard to find.

Often IF it is a wiring/connection issue a wiggle/tug test can be helpful to find the area of concern. I stress the IF there, sorry I can't be more specific obviously.

Good luck & keep us informed.

I think you are 100% correct with this being a wiring issue where a wire isn’t passing current all the time. The behaviour of the car, and the bench tested working ECU all point to a wiring issue. I have checked every single wire that would cause this issue and they all pass the test.

I could have started replacing wires, but I didn’t want to start cutting the loom when I didn’t even know if the ECU was faulty.

The plan is now to start replacing wires and see if the fault can be fixed.

I don’t particularly like this method as I prefer to diagnose things, but there’s a total of 8 or 9 wires that have the potential to cause this.

My biggest suspect is the ECU input ignition signal wire so will start with that one first, then go from there.

Thanks again!

[johnsmith222]

I cut the wire that goes to pin 7 of ECU connector B (this goes to the ECU relay pin 87). Supplying power to this wire now lets the car crank strongly and consistently. There must have been high resistance/broken wire/intermittent break to this wire.

Unfortunately in the time the car has been sitting, an additional wiring fault has ocurred. The fuel pump no longer runs. Bypassing the fuel pump relay allows the car to run.

I might just end up wiring in a switch to turn the fuel pump on. The car is towards the end of its life and I'm not sure I can be bothered doing a proper fix for this.