V40 Hot Start Mystery

DPage · Post by **DPage** » 16 Aug 2012, 09:04

My V40 has a hot start issue. I would appreciate any input as I'm out of ideas. Starts fine when cold, Runs fine, when warm, can turn off and start it immdiatley. If leave for 10-15 mintues and try to restart, turns over but will not start. Must leave it to cool - 10-15 mintues and then will start and run fine. No codes.

When it won't start, the dash temperature guage shows that the engine is cold but it is warm. The temperaure mismatch occurs with the starting issue. I assume the egine computer is thinking the engine is cold and floods it with fuel.

I've changed the temp sensor three times and checked the connections so this is not the issue. I've put in new MAP sensors abient temp sensor and a new idle control valve. Unrelated due to mileage and age I put in a new fuel pump, filter and boost pressure valve recently. New O2 sensors as well. I'm thinking it could be the wiring between the ECM and the temp sensor. Could it be a software issue or is there something simple that I've overlooked ?

DPage · Post by **DPage** » 22 Aug 2012, 13:59

More on this issue. When this happens, the live engine data readout from the ECM is that the engine temp is -40 degrees. If I turn the car off remove the key, pull and replace the positive terminal on the battery, put the key back in and turn the ignition back on without touching anything else the tempeature gauge returns to normal and the ECU sees the right engine temperature.

ECU ? Some relay somewhere I haven't changed ? Something else I haven't considered ?

DPage · Post by **DPage** » 07 Sep 2012, 15:51

More: I've taken the car to the volvo dealership which has now had it for 3 weeks running diagnostics. Can't figure it out. Changed the mass flow sensor but that didn't work. Now seems to think it may be a corroded wiring harness and is going to pull and strip the casing on the wires under the battery. If that doesn't work have told them to change the ECU. I think the cars are now so complicated no-one knows how they work. Still not thoughts from the masses. I'm going on to the 4th week at the dealer..
Anyone ?

Scrap value is fast approacing repair costs..

Post by **jimmy57** » 07 Sep 2012, 16:38

The dealer needs to look up the RTJ for the VEMS upgrade on that car. Tell them those exact acronyms and they should know what that is.
It may need a new ECM but the VEMS upgrade should be checked first as it was for ECT sensor issues.

DPage · Post by **DPage** » 05 Oct 2012, 13:26

At the end of the day a new ECU and an envelope of cash fixed this. The dealership has never seen a failed ECU before and took a long time in getting to the point where they agreed the ECU was scrap. They don't want to spend a loft of your money if theyre not sure of the fix. They also have no diagnostic software that can check the functionality of the ECU. When opened the ECU had a manufacturing defect and a pinched flex circut board with broked traces. No wonder this car has had gremlins since the day I bought it.

Tried a getting a used ECU but it was not possible to reflash the software. The dealer really tired.

The only way possible way I can think of to get around a new ECU is to go to the scrap yard and find a V40/S40 and take all the electronic modules including the key. Replace them all as a kit and the key should work as you fool them into thinking they're still in their origional car. I haven't tried it but I'd be interested in finding out if that works. Can't see why not.