C5 Suspension Pump

[Guest Doc289]

Hi guys. This is my first post, so go easy:)

This is technical question regarding the c5 suspension pump and wiring.

It would seem a weakness in these cars is a transistorized black box that mounts to the suspension pump behind the right front head light.

The transistor on my car started smoking quite badly, melted and stoped working ofcourse.

I have priced a new unit from citroen Australia.... And there has to be another way!

I have removed this transistor block from the pump motor and and fitted a 100 amp solid state relay that switches with a 3-35 Volt signal.

The problem I now have is the suspension system keeps logging a code for suspension pump open circuit or short circuit to ground. (lexia) I reset the code and it come straight back along with a "serious supension fault" on the dash display.

Does anyone know how the ecu determines this state of open or short circuit?

Failing that does anyone know how I can put the smoke back in the old one:)

Thanks for your time.

[Guest C5buff]

Hello

I think you need to read my previous posts on this subject.

Its currently on page 11 ( C5 suspension pump, pump runs continuously) Mine burnt out like yours due to a fault on the BHI ECU, the output of which put a permanent 12V run command out to the pump. As the pump is only supposed to run for a few seconds this fault soon caused it to overheat and burn out. As you will see I repaired the electric motor commutators brush assembly with parts from another old pump and then modified the way it was driven by the use of a timer. All because the cost of a new pump was outragously expensive and would have needed Citroen to fit it, together with software initialisation that would have been needed. As my pump and BHI were still ok, I had to invent a workaround to solve the problem since it was just the output stage from the ECU that was duff. Thus I avoided the costs of a new pump. The timer only cost a tenner and timer overide relay another tenner plus a box to put them in 30 quid altogether. 40 quid for an old pump to cannibalise from. Keeping the original pump and ecu meant I did not need to have any Citroen software initialisation costs either.

[Guest Doc289]

Hi c5 buff, thanks for your reply.

My BHI run signal doesn't seem to be a permanent 12 volts with ignition on. Currently it is running the pump for about a sec every 15 secs or so.

I think the presense of the fault code and the "serious suspension fault" on the dash display are stopping the system operating correctly.

I have a second hand complete BHI with control module, however it seems the transistor on this motor is faulty too! It wants to work but doesn't have the ability to supply enough current. I checked the transistors inside the black box and one is starting to burn on the board.

 

I guess what I would like to know is how the computer knows the circuit is open or short circuit?

 

In the meanwhile I'll try fitting the other BHI controller. I guess I'll have to code it with lexia.

Thanks again.

[Guest C5buff]

The fault codes would have the effect of preventing normal operation, and they will have to be reset after all existing faults have been fixed.

As you have two pumps could you not fit the commutator assembly from your original pump into the second hand pump. Fit that to the system, and then get it initialised for the car.

The open circuit/short question. It doesn't know the difference. What is probably happening is the BHI is sensing via the height sensors on the suspension that the pump needs to run to correct the trim of the car and cannot achieve it because of the fault. So it cycles on and off in a loop as its confused.

[Guest Doc289]

The fault codes would have the effect of preventing normal operation, and they will have to be reset after all existing faults have been fixed.

As you have two pumps could you not fit the commutator assembly from your original pump into the second hand pump. Fit that to the system, and then get it initialised for the car.

The open circuit/short question. It doesn't know the difference. What is probably happening is the BHI is sensing via the height sensors on the suspension that the pump needs to run to correct the trim of the car and cannot achieve it because of the fault. So it cycles on and off in a loop as its confused.

 

Hi C5buff.

 

I have spent a few more hours on the car today and I agree that there is no way the BHI could tell if the circuit is open or shorted directly. I guess since the front and rear height sensors see no change when I request lift, that is when the code is logged.

 

Strange thing is, when the door is opened and when I request the suspension to lift, the pump run command is absent. This is pointing to I believe a failed BHI (please correct is another component sends this signal or if there is a sneaky inline fuse I can't see?)

 

Thing is I have tried another "second hand" BHI and it seems to show the exact same symptoms. Either I'm missing something, or I have a failed second hand BHI as well as the pump. (Not surprising since the transistor board in the second hand pump is showing signs of a melt down)

 

I can say with certainty that if the run command was between 3 and 35 volts and was given when I requested the suspension to lift the 100amp solid state relay would work, and all other features of the suspension would work as normal.

 

Other strange thing is the check engine light has come on, permanent fault throttle pedal short to ground? Huh? Still works o.k. however?

 

Cheers, looking forward to your reply.

[Guest C5buff]

Well the run command should be about 10 to 12V. It can be checked by simply unplugging the connector and measuring with a voltmeter whenever the door is opened or ignition is switched on, the signal should appear for a few seconds. Also check that the main power is present by next unplugging the power connector and this should have 12V on one pin all the while the battery is connected. Check that the other pin goes to chassis and that it is a good connection to the bodywork. Being careful not to short them out. If no power then next check maxi fuse MF8 located in the engine fuse box it is a big one 40A. NB// If you ever unplug the multiway connector on the BHI with the battery still connected then you will get a major suspension fault indicated in the cockpit, which will require resetting by Citroen or if you have your own Lexia with that, before you can proceed with anything.

With regard to fitting another BHI it will have to be initialised correctly as the BSI and security system won't recognise it. So they won't work with it.

No idea what the throttle thing is about.

[Guest Doc289]

Well the run command should be about 10 to 12V. It can be checked by simply unplugging the connector and measuring with a voltmeter whenever the door is opened or ignition is switched on, the signal should appear for a few seconds. Also check that the main power is present by next unplugging the power connector and this should have 12V on one pin all the while the battery is connected. Check that the other pin goes to chassis and that it is a good connection to the bodywork. Being careful not to short them out. If no power then next check maxi fuse MF8 located in the engine fuse box it is a big one 40A. NB// If you ever unplug the multiway connector on the BHI with the battery still connected then you will get a major suspension fault indicated in the cockpit, which will require resetting by Citroen or if you have your own Lexia with that, before you can proceed with anything.

With regard to fitting another BHI it will have to be initialised correctly as the BSI and security system won't recognise it. So they won't work with it.

No idea what the throttle thing is about.

 

Hi again C5buff,

 

I have checked all the main fuses power supply and earth no problem. If I manually trigger the solid state relay I have fitted the pump runs no worries. However If I allow the car to control it, all it does is pulse for 1 sec every 15 seconds.

 

I have also checked the command wire with a multimeter and it shows 12 volts for 1 sec say every 15 seconds. There is no prolonged 12 volt pulse when the door is opened, ignition is switched on or raised height request from the switch in the car... It just puts 12 volts to the command line in the same pattern.

 

Perhaps when I installed the other BHI it was not recognized. Has anyone initialized a second hand BHI with lexia before? If so i'd love to know exactly how to do it:)

 

 

Thanks so much for you patience.

[Guest C5buff]

Hi Doc

I don't have a Lexia yet, so I don't know if it can initialise a different BHI as the security system is involved. Anyway if the current BHI ECU works the suspension ok with you switching your own 12v run command then you can get away with using a timer to do the job for you as per post on page 11. All that is required is to switch 12v on the command line for about 6 to 10 seconds every 15 to 20 minutes in order to keep the pressure up, as you say you can do this already manually, and the pump runs. You will of course have to reset the existing fault codes first to get the BHI to play ball, and run the suspension.

[Guest Doc289]

Hi C5buff,

 

I now have the full answer to this problem.

 

It would seem the original BHI in my C5 has failed in such a way it caused the pump to run overtime and caused the control transistor on the pump motor to burn out. Later when the BHI cools down it fails in a way that stops it running in certain instances. (Causing the "Serious suspension fault" to appear on the dash display)

 

The second hand pump I was supplied firstly had also failed, both the BHI and the transistor were failed in that unit also.

 

I was supplied a third pump and BHI unit complete and bleed the system with the info found in my other post.

 

No BSI programming was required. (In this instance)

 

Moral of the story: Second hand pumps and BSI units on early C5's (They changed these to another style in later years) are likely to fail. Make sure you buy one from a reputable dismantler, or have some warranty!

 

I hope this helps members and other people going through the Suspension pump drama.

 

All the best Doc289

[Guest Doc289]

Forgot to mention, The check engine light extinguished when the good working BHI was installed.

 

It seems to be likely you have a failed BHI, if fault codes for faulty throttle pedal sensor and open or short circuit in suspension pump motor appear at the same time.

 

However, as mention on this forum, The BHI can fail in some strange ways i.e. Constant power to pump, no power to pump, no run command when door is open in the morning etc, etc.

 

Cheers.

[Guest C5buff]

Yep that all makes sense, in my case it is just a permanent run output command the BHI being ok in other respects ie it still worked the suspension. This problem cannot now ever cause a burnout on my pump because the timer prevents it.

It would even be an idea to safeguard a currently good pump since the timer could be set up to only allow a 15 second run max before it cut off thus guarding the pump motor. At least then you would have no burnt out wiring or other damage to the motor even though in would mean the BHI output was duff.

Well done Doc for sticking with it and solving the problem and thanks for reporting the results back to the site so we can all benefit from what happened.