Astra H VXR Sprint

After fitting another UEC, the non start issue where the fuel pump was not getting a 12v feed appeared to have been solved. Certainly for around 4 months, until it reared its ugly head again.

With a direct feed to the pump, the pump ran so again no issue there with the fuel pump itself. So the next thing was to remove the UEC and take a look. Upon inspection, X2 pin 56 in the UEC (fuel pump feed) was showing signs of corrosion which was not there previously. Swapping the UEC to another car proved that the UEC was not at fault and was working fine, which then suggested an issue within the wiring somewhere. Luckily Vauxhall/Opel factory wiring diagrams make it easy to identify what goes where within the UEC and associated plugs. Read more

An intermittent fault is somewhat tricky to diagnose and identify the cause until it becomes a permanent fault! So an intermittent non start was going to be entertaining to find as it could be electrical or fuel related. Additionally until rectified it meant trackdays had to be put on hold for obvious reasons.

After three weeks or so of using the car daily and having the non-start occur a couple of times, it eventually became a permanent non-start. Finally that gave me something to look for. Eliminating the crank sensor (they are occasionally prone to failure), as a crank signal was still present during cranking, it turned out that there was no fuel at the rail, and the fuel pump was not working.

Checked and tried a second known working fuel pump relay, not that. Removed the housing to check the pump in the tank; with the pump out of the tank, 12v from a second battery and the pump ran fine. So the pump was ok, which was good news as I have never seen a failure of an aeromotive 340 fuel pump to date. Next check all the fuel pump wiring in the housing, all ok.

Initially bridging/bypassing the fuel pump relay in the UEC (Underhood Electrical Centre) and the pump would run, so next check through the car loom from the UEC to the pump and the wiring all checked out ok for continuity. Also checked the 4 pin plug under the car next to the tank, in case it had suffered from corrosion.

So could it be the UEC? Fit another ‘slave’ test UEC, programme to the car, and fit the fuel pump relay and turn the key. Fuel pump primes and the car fires into life.

So problem solved, a fault within the UEC. Originally fitted with a UEC with Ident GR, a secondhand UEC from a 2010 car within the same Ident range (Ident LP) was sourced from a mate who runs a breakers for £50 which has since be fitted and programmed to the car and all is well.

Uunderhood Electrical Centre:
Vauxhall/Opel: UEC Part Number: 93184656 Ident GS Production Number: 13206746
Also Services Idents: GR GT GU GX GY GZ HA HB HC LM LN LP LQ LR

When sourcing a second hand unit ensure it has been correctly reset on Tech2 (or similar) for reprogramming.

UEC Ident LP

Towards the end of last year, occasionally at start up the dials would drop out and then do their ‘VXR’ reset sweep and various dash lights would come on. Then once it had ‘reset’ itself everything was fine. Also from time to time the car would not turnover, not recognising the key, and so would not start. It didn’t cause any issues but was something that would need further investigation at some point.

That point has arrived with the instrument panel now resembling Blackpool Illuminations almost all of the time…..

Various dash lights illuminating either at random or all at once, rev counter dropping out and then carrying out the ‘VXR’ reset sweep and returning to normal opration, fuel gauge dropping to empty, headlights coming on with the headlight switch in the ‘off’ position, headlights coming on as expected when switch on but then failing to go off when the switch was turned off, rear lights coming on at random, indicators sometimes refusing to work……. Additionally sometimes the car would fail to start and the management light would flash, indicating an immobiliser problem which is part of the CIM module.

A quick check on Tech 2 listed many communication errors between all of the modules on the car (see post below for DTC’s) – CIM (Column Integrated Module), REC (Rear Electrical Centre), UEC (Underhood Electrical Centre), ABS/ESP (Anti-Lock Brake and Electronic Stability Module), and ISP (Instruments) which meant tracing the problem would be down to systematically checking the common error codes on TIS and working through and checking each module to eliminate them one by one.

Where to start?

Initial thoughts…. It was the CIM playing up, not uncommon on Astra H. While swapping one isn’t that difficult to do, it is quite involved so due to all the trouble codes it was worth checking the other modules first.

UEC: Water Ingress in the UEC can cause issues, but after unplugging and checking this was all ok, so the contacts were given a clean and grease to prevent any future problems.

REC: There were few DTC’s relating to lack of communication between the REC and UEC, REC and CIM and REC and ABS/ESP. The REC is easy to change as there are only 6 electrical plugs to remove and a single bolt holding it into the car. I had a spare REC to hand so it was worth trying it to eliminate it. The original REC was reset on Tech 2, battery disconnected and then removed and the replacement REC fitted. The replacement REC I had was from a later 2008 car but compatible as it was in the same ident range. The new REC was programmed on Tech 2, VIN entered and coded and all worked fine, however after some testing the same DTCs were present suggesting that the problem lay elsewhere.

CIM: As stated earlier the CIM units are known to cause issues, so having looked at the UEC and REC the next option was to try a replacement CIM module. The occasional loss of communication between key and CIM suggesting an immobiliser issue pointed strongly towards the CIM unit as well. Slightly more involved to replace unlike the REC and UEC as the airbag and steering wheel have to be removed to access the CIM and it needs resetting prior to removal and reprogramming again (using Tech2 or similar), but I had a spare second hand CIM to try so it was swapped onto the car, and after reprogramming all the troublesome DTCs had gone and the instruments appeared to be functioning normally.

A brand new CIM unit has been ordered (thankfully they are not too expensive at trade price!) and will be swapped over before the first track day.