Accelerometer

OK, I won't bore you with details but, I finally plugged into a Lexia and got a list of codes as long as my arm, several of which relate to the accelerometer which is not sending a signal at idle, not resetting the injectors and something else related which eludes me.
Q. what is an accelerometer, where is it, what does it do, and, is it serviceable?

Hi Bill,

I finally plugged into a Lexia and got a list of codes as long as my arm,

The trick with lexia is to delete all the codes and then run the car around to get fresh codes. The reason being is some could be very old and no longer relevant. This saves chasing non existent faults.

As for the 'Accelerometer', I think this is a translation from french, rather than an Accelerometer in the english sense.

I would suggest the detonation sensor, but it not going to be a faulty sensor, more likely the injector didn't fire when its was expected to.

These readings were after a reset! and all came straight back, on re starting, without even moving the vehicle.

It's my understanding that the accelerometer detects movement on all three planes and that it relates to anti-lock systems, determining which wheel to unlock and when, depending on the directional forces as well as the ABS sensors themselves, and possibly also relating to engine management systems when it detects the vehicle is idling ie not accelerating or decelerating, and possibly triggering the airbags in the event of extreme acc or de ccelerating. I have no doubt there is one, somewhere, just wondered where it was so I can hit it with a big hammer, it always used to work, back in the day........

These readings were after a reset!

I am not sure what got reset, but to clear the codes you need to delete each one and archive the faults against a reference and mileage (or km-age)
You may not be able to clear the permanent faults, but the non-permanent ones will disappear, which can make the list considerably easier to manage.

the 'accelerometer not resetting the injectors' fault sounds very much like a non permanent fault and I believe it occurs when the engine is running and injectors are giving trouble.

My suggestion is to clear the codes out by archiving them (as described above) and try again, you will save yourself looking at stuff that doesn't need looking at. If you would like some better, more step-by-step instructions, I can dig out lexia and fire it up, but a pub lunch is calling me now.

It's my understanding that the accelerometer detects movement on all three planes and that it relates to anti-lock systems, determining which wheel to unlock and when, depending on the directional forces as well as the ABS sensors themselves, and possibly also relating to engine management systems when it detects the vehicle is idling ie not accelerating or decelerating, and possibly triggering the airbags in the event of extreme acc or de ccelerating. I have no doubt there is one, somewhere, just wondered where it was so I can hit it with a big hammer, it always used to work, back in the day........

While I agree with your explanation of the english word, I think you may not find the accelerometer that the fault refers to as I think its a french mistranslation and nothing to do with ABS/Traction control/ESP. I am happy to be proved wrong

It would be nice to see the 'P' codes with their description from the lexia, (Use ALT and Prt SC, then open 'paint' and choose Edit, Paste) to capture each screen

I hope this helps, its a post from the diesel section of the forum which correctly identifies the 'accelerometer' in the lexia description as a 'knock sensor', I used 'detonation sensor' in my post, but they both achieve the same end result.

Hope_it_works_out wrote:The starting point is defo obtaining the fault codes in the ECU. I have the codes for my faults and it is basically open circuit on inj 4. There is also a fault relating to no periodic resetting by the accelerometer (knock sensor), that one is there because the sensor does not detect detonation on cylinder 4 so the ecu prohibits the resetting. So my problem is either a blown transistor within the ecu that controls the pulse to fire no 4, wiring issue, or a control input failure to the ecu. Will keep you updated Im at citroen on Thursday.

As for its location, I think is at the back of the engine, on the block, under the air filter (16v engine). I will try and dig up some pictures, but its unlikely that this is the part that needs the hammer

The knock sensor (accelerometer) location on a Citroen C3 1.4 16v HDi Marked 1120 on the picture.

OK seeing as you ask

P1160 Turbo Pressure low

P0704 clutch switch, no signal at idle

P0401 Low EGR pressure

P1363 Accelerometer, no signal at idle

P1351 Plug relay, Plugs not supplied

P1163 No resetting by accelerometer, no periodic injector setting

P0500 Speed received by CAN incorrect.

The last one relates to an ABS sensor which has now been replaced, the rest would leave you to believe the vehicle was a basket case and yet it is starting and driving fine with no MIL on for several hundreds of miles, no problems with starting, occaisional stalling when in neutral and coasting, possibly the clutch switch.

If as you infer, the injectors weren't being reset then I would notice if one wasn't injecting as it would be lumpy at least? it runs smooth, ticks over fine.

If it weren't for all the other problems I'd sell it whilst the light was out!! but as it is, whos going to want a car with no wipers, no heater and a failed wheel bearing?
Don't all shout at once

Just a thought............

If I had inadvertantly switched injectors during engine transplant (which is highly likely!!!) then might it be upset that it can't detect them firing because its looking at injectors that aren't firing but are on another stroke? And if that were the case, can I (using the Lexia) re-educate the ECU as which injector is in which cylinder?

can I (using the Lexia) re-educate the ECU as which injector is in which cylinder?

YES!

just like this

The numbers in the boxes are the numbers written on the injectors.
They are fine tuning for the actual injector characteristics due to the manufacturing tolerances.

then might it be upset that it can't detect them firing because its looking at injectors that aren't firing but are on another stroke?

No,

the injector is addressed by its wired connection and not its number. If you managed to switch the wires between cylinders, then this could happen, but its not something that can be done accidentally in the real world.

So.............Thinks...................Thinks some more........... can the difference in tolerance between injectors explain the accelerometer not detecting them, even though they are within the tolerance required to run the engine?