Anyone know anything about Bosch Motronix ECUs?

[RustyNuts]

This is the ECU I have in the renault safrane that has been off road for a few years. Great car, underrated and victim of badge snobbery but it has so many toys that it still puts a smile on my face after so many years. It's also worth sweet FA so unlikely to get nicked.. and being a renault automatic... well even more unlikely lol.

 

Now it has a problem and so far i've not got any real help elsewhere so thought i'd try here for general advice.

 

It had a failed coil for the ignition (only one coil as its a 5 cylinder engine so the induction is wasted). According to some isle of wight ECU repair company website, if the coil fails it has a habit of fucking over the ECU. Well three guesses... and when i spoke to the company on the phone they weren't overly helpful except to tell me they did encounter it once but it was a wiring loom fault.

 

The car starts, runs, idles, moves.... but the cooling fans won't activate at the required temperature. Now there are two sensors and both appear to be working - one shows the temperature on the dashboard (working) and the other seems to be connected directly to the ECU and I concluded from a test that was working too (did a resistance check at hot and cold if i remember right).

 

So.. I checked out the wiring diagram for the loom and tracked down the circuit wire for tha fans. When grounded the fans activate in both low and high modes so no relay glitches there. What I did notice though is that sometimes the car will start and instantly idle at 400rpm instead of 1300 and it will activate both fans - safe mode to protect against overheating so it is clearly able to output a low signal to the relays down the loom - when it chooses.

 

So i've concluded that the ECU is shot. It's no longer available from renault and is coded to the keys, dash.... various others making it not so easy to swap for another.

 

Any ideas out there please?

 

Rusty

[hauserplenty]

Maybe you could buy one of those aftermarket cooling fan kits, which comes with a sensor, and relays and all the wiring you need, and bypass the existing fan circuit? You may wish to check the coolant temperature sensor, to confirm your diagnosis before spaffing top wonga on an ECU. Since the keys are coded, so much for bunging a mega squirt DIY unit in there...

That limp home fault points to a faulty CTS. You need a table of resistance values to know what values it expects for a given temperature. Then you can either bypass it with a fixed resistor, go for a blag and see what you get, or build a whole new circuit for the fan.

Or put a switch under the dash, and click it when the temperature gauge rises. But that seems a bit shit. Too shit for autoshite.

[spike60]

 
"Or put a switch under the dash, and click it when the temperature gauge rises. But that seems a bit shit. Too shit for autoshite."

 

 

I'll think you'll find it isn't!

[fordperv]

Are you definately sure there's not a radiator fan switch knocking about? Check all around the radiator, I only ask because the cts will tell the ecu what temperature the coolant is so the ecu works it's magic with fuelling and the temp sensor for the clocks tells the clocks what temp it is, I have never touched a safrane I'm just thinking logically

[spartacus]

If it runs on the ECU it's got and the only issue is that the fans don't turn on then put them on an independent circuit, as suggested. It's nice to get things right but as you've already pointed out it's going to be nothing short of an expensive nightmare by the sound of it. Enjoy it while it runs!

[Asimo]

Doubt this is an ecu issue, it does everything important after all.

Re the fans and idle sometimes high - does this depend on whether the AC is selected?

 

I would fit a thermo switch and a manual override.

[Lacquer Peel]

Does it have a separate fan module? My 405s with air conditioning did.

Seems a bit much to write the whole ECU off.

[Station]

I'm pretty sure the sensor you talk about is not connected to the ECU. The ECU doesn't operate the fans. There should be another sensor on the rad maybe?

 

My Motronic ECU doesn't control auxillery stuff.

[RustyNuts]

Maybe you could buy one of those aftermarket cooling fan kits, which comes with a sensor, and relays and all the wiring you need, and bypass the existing fan circuit?

 

<snip>

 

Since the keys are coded, so much for bunging a mega squirt DIY unit in there...

That limp home fault points to a faulty CTS.

 

<snip>

Or put a switch under the dash, and click it when the temperature gauge rises. But that seems a bit shit. Too shit for autoshite.

 

I can make an aftermarket cooling switch using an arduino processor and temp sensor connected to it - hook it up to some relays and write the code and bobs my uncle. I also need to hack up a spare wiring loom i have which i was hoping to avoid... but spares are for using so it'll have to do. I just wanted to see if i was missing anything that someone else could think of before proceeding.

 

The safety mode is to stop the engine overheating but it typically kicks in when the ECU is unhappy about something - battery that has drained flat and then been jump started for instance. If i disconnect the battery and reconnect it then jump it the fans bahave. It's all very quirky.. but it is french!

 

The under dash switch was also on my mind so i bought some RF transceivers to work with my arduino bodge so that i can remote control it if need be without wiring. Love my gadgets... lol

 

Are you definately sure there's not a radiator fan switch knocking about? Check all around the radiator, I only ask because the cts will tell the ecu what temperature the coolant is so the ecu works it's magic with fuelling and the temp sensor for the clocks tells the clocks what temp it is, I have never touched a safrane I'm just thinking logically

 

Definite. The ECU grounds the relays that are next to the fan motors - if i unplug the wiring loom behind the headlight and ground them manually the fans are activated in the same way. I've also had the engine out a few times (requiring the removal of the front of the car including the fans) so i know it pretty well. Would have been nice if you were right though!

 

Doubt this is an ecu issue, it does everything important after all.

Re the fans and idle sometimes high - does this depend on whether the AC is selected?

 

See I couldn't fathom that out either. The ignition coil went pop so why didn't the ignition part of the ECU? (knowing my luck that will fail now i've said it). Anyhow it still starts and runs... behaves well in that respect its just been a right royal pain in the arse with the cooling. It overheated to the red line once and i suspect the HG has also failed (creamy oil not looking hopeful) but i have a spare engine i can chuck in. I just need to get to the bottom of the cooling first.

 

Oh and it idles low - 400rpm instead of 1200 and no AC gas in it at the moment but thats never made any difference - it's still been intermittent with the fans (yes the did work sometimes but then completely gave up).

 

Does it have a separate fan module? My 405s with air conditioning did.

Seems a bit much to write the whole ECU off.

 

No seperate module and the ECU ain't being written off - i can't afford to replace it lol, i'll just have to live with a bodge but i was just hoping someone else might have a last ditch idea lol.

 

I'm pretty sure the sensor you talk about is not connected to the ECU. The ECU doesn't operate the fans. 

 

The sensor is connected to the ECU and does operate the fans - I have a renault maintenance document (and book) clearly showing this. The ecu takes the temp from the engine not the radiator (makes sense really seeing as the engine is the most important part and at risk of overheating) and then does the fans when needed. The radiator isn't really at risk of overheating so why they put the sensor there on other cars is beyond me lol.

 

Well looks like i'm stuck with a bodge then 

[twosmoke300]

Bba reman or ecu testing could test and repair your ecu

[SiC]

Tried connecting a Variable Resistor to the temperature sensors for testing it? Can then turn it right up and see if it does kick in at what would be OMGHGF temperatures.

[RustyNuts]

No I never tried that as it matched the resistances that the manual stated at both hot and cold. I think there was another tell tale that it was working too but i'll be fucked if I can remember what after all this time lol.

[SiC]

I was more thinking in testing if its set to really, really hot (I.e. far more you'd ever want to get an engine too) and see if the ECU decides to eventually kick the fans in.