An unwelcome ECU connector suprise

Post by **CitroJim** » 01 Sep 2008, 07:43

red_dwarfers wrote: It does feel like that the xant runs smoother with more poke, but thats probably just me wanting it to

Well it certainly did a great job in getting you to Stratford Kev

I was, for reasons unknown

, thinking about your fast idle problem this morning. I was talking rubbish at the show, the electrovalve is doing exactly what it should as the Lexia said that fast idle was in operation despite the coolant being up to temperature. Basically, as soon as the coolant hits 60 degress, fast idle should cease.

The sensor that measures the temperature for ECU idle control purposes is the green one on the thermostat housing. It'll be worth checking the connections to it but I wonder if one or other of the corroded ECU connectors is causing it. I'll look in the wiring diagrams later and see which pins bring the coolant temperature into the ECU and see if they correspond with the bad ones.

It needs fixing as the ECU may be thinking the engine is stone cold and thus using cold-running maps which may knock fuel economy about a bit. Mind you, it may be what is making it appear to go well

The temperature gauge runs on a different sensor, the blue one.

red_dwarfers · Post by **red_dwarfers** » 03 Sep 2008, 19:34

I got around to rewiring the ECU connector last night, suffice to say i've now run out of insulated crimping connectors now!
Doubled checked out all the connections to make sure they are all making contact and crimped properly.
Still getting perminant fast idle

Just for reference - the dash temperature gauge sensor is also the one to let the coolant run through to the rad at the right temp I take it or is that a seperate sensor/thermostat again?
It does look like the green sensor on the Thermo housing could need some attention then, or the wire from the sensor to the ECU.

JIM
If you do have a bit of time at some point, is there any chance you could take a peek through you new manuals to see which contact it is for the fast idle temp sensor?

deian · Post by **deian** » 03 Sep 2008, 19:45

Mr Dwarf,

That connector is a bad sign, it would explain any problems you've had in the past.

Myself, I would firstly find out WHY the problem happened in the beginning? Is the seal leaking in some rain water (green corrosion), and then making another pin work harder (burning out, the brown one), or does it lead from somewhere else? Maybe go find a pin out map for the ecu/connector and see what the affected pins do. Obviously, that is what I would do cos i'm that kind of guy, why it happened may help others prevent it.

Funny thing is, when people get engine management problems, who would think about checking the ecu connector.

Obviously it's fixed now, thankfully.

Post by **CitroJim** » 03 Sep 2008, 22:06

red_dwarfers wrote:JIM
If you do have a bit of time at some point, is there any chance you could take a peek through you new manuals to see which contact it is for the fast idle temp sensor?

Kev, I'll do better than that, I'll scan the diagram and post it up with a brief explanation of how to read it. Do you have a BoL to save me needing to identify each component? Each component is referenced by a four digit number (e.g. ECU is 1320) and luckily, the BoL contains a comprehensive list at teh start of their take on the wiring diagrams.

Just found the circuit you need in Volume XVIII. Seriously, there are four thick volumes just of wiring diagrams

Tellingly, they're the most dog-eared of the whole set

Post by **CitroJim** » 04 Sep 2008, 20:55

Kev,

Here are three links to the circuit diagrams for the XUD9TF Injection ECU.

The First Diagram is the schematic circuit.

The Second Diagram is the harness diagram. This shows the harnesses associated with the first circuit and which components run in which harnesses.

The Third Diagram is the physical location diagram which shows the harness runs and component locations in the car.

For your problem, the ECU is Component 1320, the Temperature Sensor is 1220 and the Idle Electrovalve is 1232.

The harness diagram shows the wiring from the ECU to the Temperature Sensor and Electrovalve runs in harness 21JN which is the one that runs from the ECU, across the engine and up to the electrovalves on the bulkhead. On the schematic and harness wiring diagrams, the wire number is that printed on the wire itself and the number in the small square boxs on each item is the connector pin number. The bold designations by the component connectors is the connector colour and number of ways. So the idle electrovalve for instance has 2V VE by the side of it. This means a 2 pin green (vert) plug.

The boxes that begin with a bold E on the harness diagram designate earth (Equiponential) points. The location diagram show where these actually are.

To test the Coolant Temperature Sensor, use an ohmmeter to measure its resistance. Look for a resistance of about 2.7K at around 18 degrees.

Hope that helps...

Note, These are big pictures of about 700K each. They need to be this big to retain the fine detail. Please be patient whilst they download from my slow web server connection.

deian · Post by **deian** » 04 Sep 2008, 21:35

Whoa, check out how snakey and insane the wiring harness is, imagine having to rewire a new harness in! Holy moly!

Good scans there Jim. Where dya get them?

MikeT · Post by **MikeT** » 04 Sep 2008, 22:24

red_dwarfers wrote:I got around to rewiring the ECU connector last night....
Still getting perminant fast idle

I've intentionally isolated this because I can't be bothered to read the whole thread again

There are several methods of fast idle operation but the most common method employed on the Bosch pump is also the most unreliable and the symptom is, oddly enough a permanent fast idle. It's my bet that your fast idle system has failed, in particular the above mentioned (1232) electrovalve is dead.

If this is the cause, I'll also bet it's coincidental to the ECU connector damage shown rather than because of it.

wheeler · Post by **wheeler** » 04 Sep 2008, 22:42

citrojim wrote:The boxes that begin with a bold E on the harness diagram designate earth (Equiponential) points. The location diagram show where these actually are.

The boxes with E are splices in the harness where wires join together & they are used for lives awell as earths.

Post by **CitroJim** » 06 Sep 2008, 11:38

MikeT wrote: If this is the cause, I'll also bet it's coincidental to the ECU connector damage shown rather than because of it.

That is very true Mike!

I ran a diagnostics session on Kev's car and the ECU is asserting fast idle even when the engine is hot as far as I could tell, hence the suggestion to initially test the CTS and ECU wiring in looking for the fault. The electrovalve is far from above suspicion as they suffer the same fate as hydractive electrovalves in that their back-emf diodes go open-circuit and upset their operation.

Thanks Wheeler for the full expanation of the "E" boxes!

deian wrote:Good scans there Jim. Where dya get them?

From the pukka Xantia Workshop Manuals Dei

Any that are desired, let me know!

wheeler · Post by **wheeler** » 06 Sep 2008, 12:04

Was the CTS reading a normal values on the lexia paramiters screen ?
Its not unknown for the temp sensors to leak into the plug & capillary action draws the coolant up the wire & into the ECU, does the ECU connector smell of coolant ?
Are the fast idle & EGR electrovalves not the same ? cant they be swapped to check operation ?

MikeT · Post by **MikeT** » 07 Sep 2008, 12:16

wheeler wrote:Are the fast idle & EGR electrovalves not the same ? cant they be swapped to check operation ?

The connectors are different and cannot be swapped straight off but I think a bit of cutting/filing could make it happen. Chances are if one of the valves failed, the other would have failed or soon will.

The capillary theory is an interesting one and I'll be checking my ECU connectors next chance I get!

red_dwarfers · Post by **red_dwarfers** » 07 Sep 2008, 21:16

Thanks for the immense response!
Citroen fast idle tinkering will commence on Saturday, if not before

I actually had a tinker around with the ride height today, done some measuring and that, and come up with a problem. My face was

when I did a search for relevant topics, its going to take a lot of reading!

davek-uk · Post by **davek-uk** » 08 Sep 2008, 12:21

There is an easy way of telling if the fast idle solenoid is duff - simply put a bit of pipe directly from the cam vacuum pump to the fast idle diaphragm on the fuel pump. This way you have direct suction and constant cool running. My Xantia has been like this for a few years and I haven't had cold starting problems even in the dead of winter.

Dave

red_dwarfers · Post by **red_dwarfers** » 20 Sep 2008, 22:38

Sorry dave, only just read your post...I'll have to try that tomorrow

I've had another look at the fast idle problem (bit of info in my blog) and it seems that on a cold start (under 60 degrees) it idles at around 950 rpm and if left to idle, the needle will gradually make its way up to around 1050 or so and stays. If again starting from under 60 degrees I 'accelerate' a bit and let it idle it goes straight back to 1050.

If you have a look in my blog you will also see that the temperature on the green sensor right up to the ECU connector is showing within the tolerance of Jims resistance. So maybe I cleaned up the green thermostat connectors the ECU is now doing the right thing and it could be the output side of the ECU? that still doesn't sound right.....

Post by **CitroJim** » 20 Sep 2008, 23:28

Kev,

Forgive me for I've been leading you astray here

I have a real blind-spot for some things and 1.9TD fast idle is one of them. Ask MikeT!

In fact (if I'm right this time) fast idle is the default and the electrovalve is switched ON for normal (warm) idle. Hence why the Lexia shows a 1 condition for the fast idle condition when up to temperature. It's negative logic

A 1 meaning the electrovalve should be on. This means you should see zero volts across the electrovalve coil when the engine is cold and this should change to a voltage (may not be a full 12V) when the engine is at normal temperature. If I'm right (and I'm still not sure I am) this should translate in no vacuum at the actuator for fast idle and vacuum for normal warm idle.

As I say, I have a real blind-sopt here