C5 HPi Problem with Error Code P1631

[birstall]

I took my car in to a local mechanic to get the clutch done.

When I went to pick the car up on Saturday, they told me they had done the clutch OK but now had a new problem with the car and had spent hours trying to fix it to no avail.

I suspect the following has happened based on what he's told me.

1. They reported an immobiliser fault massage when they tried to start the car after reconnecting the battery. I suspect the guy doing the repair wasn't aware that you had to retune the key in after disconnecting the battery.

2. He then says he "fiddled" with the wiring to the ECU unit and managed to get the car going. It then drove OK for a trip but then cut out.

3. When I got there the owner was making disproportionate complaints about the state of the wiring to the ECU and making a big issue about the ECU not being fixed down in the plastic housing.

4. I've owned the car for about 6 years and never had a problem with the ECU. I suspect they've done something nasty when they were having problems getting the car started.

He said his Snapon diagnostic reader wasn't working. I went home to get my own bit of kit and found a P1631 error message, meaning there's now a fault with the ECU processor.

I'm now wondering if the actual processor chip is on a separate card which might have been shaken loose when they were fiddling with it.

Does anyone have any experience of this?

Thanks

Pete

[RichardW]

In order to do the clutch on a C5 you need to remove the main ECU box, and to do this you need to remove the main power feed. This is connected to a meaty looking M8 post. However, the post is only on a thin strip of copper which is then glued into the main power board. It's easy (ahem... C5 clutch change trouble) to break the power supply off the board when re-building it. I would whip the cover off the box and check to see if the post is waggling about. A new unit is >£200 but AFAIK it's not coded to the car, so a scrappers unit should be able to used. It is also common to the C4 I think.

[birstall]

Richard

Thanks for the reply.

Is it possible to repair this or does it mean a replacement unit.

The garage are planning to send it off for repair.

Is this appropriate?

Cheers

Pete

[RichardW]

My mate looked at it, but it appeared to go into a mass of resin and there appeared to be some circuit boards around it, so he decided a new one was the way to go - he needed the car back up as a new sprog was imminent!! A specialist electronics repair co may well be able to fix it.

This is the bit: e-bay fuse board

The +ve post is in the middle at the top. There appear to be be 2 types on early cars, if the unit in the link is Siemens, then it's for later cars. RP 9095 is 03/10/01 - so most will be Siemens:

6500 Y1 01 FUSE BOX DELPHI
- UNTIL RPO No. 09095
6500 Y3 01 SIEMENS
- SINCE RPO No. 09096

Note that my experience was with a box fitted to a MK2 C5, and it looks a bit different, but the post is there alright....

[birstall]

Thanks for that.

I'll try and have a look at it myself before they send it off for repair (if they haven't sent it already).

Will let you know how I get on but may not be able to look at it until Saturday.

Cheers

Peter

[birstall]

Here's an update on the C5 HPi.

The mechanic didn't seem to be getting anywhere. He couldn't source a second hand ECU and Citroen no longer stock the part as new (but would cost £850 new anyway so not an option) .

I took matters into my own hands and purchased another faulty C5 HPi for £350 off gumtree from someone local.

The car has only 54k on the clock but needed a new coil set and was out of tax and MOT.

The mentality behind this move is that my own car is fully operational apart from the ECU so I can fix any problems with the new car with bits off my own (in theory), and then scrap the old car.

So the mechanic agreed to sort me out with the new car since he couldn't fix the old one and not charge me for the work done.

The car passed its MOT OK after swapping the coil over and was fit to drive.

However a number of other issues need tackling to improve overall performance.

Other faults found with the new vehicle:

- Steering column universal joint worn and rattling. Now fixed by swapping columns over - done myself.
- Both lambda sensors faulty. Mechanic swapped these over for me.
- 2 tyres fairly worn. Remedied by swapping two good tyres off old car.
- Some bubbling noticed on alloys of new car. Considering swapping these over from the old car. Mechanic has SnapOn computer to reprogram tyre pressure sensors.
- Air Bag fault message coming up intermittently (think this could be dodgy connector under seat after reading previous posts).

In addition, I've retrieved both of the fuel pumps and the EGR valve off the old car so I can fit to the new one, although not needed at the moment.

The car seems to drive well - noticably better than the old car.

In summary, a reasonably good result, although it has obviously taken up a lot of my time in arranging the solution. But I have the bonus of a newer car with a lower mileage.

Personally I like the car. The HPi engine has got a bad reputation, but in my opinion it's a nice car when it's up and running properly.

Some of these problems are ones you could encounter on other used vehicles of a similar age.