No ground from PCM

1st October 2015, 13:12

Hi,
I have a Citroen Xsara 1.6i 8V (yeah, I know it's not Saxo but as a last resort I have to try) and I have no ground from the PCM/ECU. It's a Bosch mp7.2 03 ECU.
The longer version...
The car runs like crap, barely starts in the morning and uses TOOOOOO much fuel. When I tried to measure the values at the sensors I got no ground from the MAP, Stepper motor, IAT and TPS.
Maybe someone can help me with a pinout for the ECU or a procedure how to rule out if it's wiring or ECU fault.
Thank you in advance.

1st October 2015, 15:23

plug a diagnotics machine in. Probably the wiring as the car should not start with a faulty ecu

1st October 2015, 19:28

Can you at least tell me on which pin/s is the ground/s that goes TO the PCM so I can test voltage drop. When I turn the key to ignition on (engine off) i get 3.8V on the ground wire for the MAP that comes FROM the PCM. Also, on the stepper motor (4 wires) i have 12.8V - 5.7V - 12.8V - 5.8V. I pretty much have no ground on any sensor so my idea was to cut the ground wires for the sensors close to the PCM plug and check the voltage on the PCM side, if it's OK, then I must have some short in the wiring. It sounds like a crazy idea but I really don't know how to diagnose this.

1st October 2015, 19:40

All of he wiring diagrams are on here simo the site owner posted them up yonks ago,have a search.

1st October 2015, 20:24

This mayhelp of google images
http://www.autoelectric.ru/auto/citr...xo/nfz/nfz.htm

1st October 2015, 20:48

Quote:

Originally Posted by vincent1

This mayhelp of google images
http://www.autoelectric.ru/auto/citr...xo/nfz/nfz.htm

Thanks man, I found this but my ECU utilizes all 3 rows of pins, I'm guessing it's not the same diagram, right?

1st October 2015, 20:52

With the plugs disconnected, you can't get a reading. All the voltages you see in diagrams etc are taken with the sensor and plug connected.

This is why you can't "find" a ground point on any of the pins.

Also, on a side note, why would you cut the wires? If you're checking for a short use a resistance test between the plug i.e unplug the ECU, and the sensor

for the map sensor and most other 3 pin sensors, the ground pin is no.2.

1st October 2015, 21:02

Quote:

Originally Posted by MartinObviously

With the plugs disconnected, you can't get a reading. All the voltages you see in diagrams etc are taken with the sensor and plug connected.

This is why you can't "find" a ground point on any of the pins.

Also, on a side note, why would you cut the wires? If you're checking for a short use a resistance test between the plug i.e unplug the ECU, and the sensor

for the map sensor and most other 3 pin sensors, the ground pin is no.2.

I measure on the sensor side backprobing the connector, with ECU plug on and key to ignition. In that case I get 3.8V on the ground pin and 3.6V on the signal, even if I got it wrong, there is still voltage on all 3 wires. The ref 5V is ok. I thought of cutting the ground wires so I can eliminate the "shortage" problem and measure the ground as close as possible to the PCM. I know, it's stupid, but even then, I'm not that stupid to do measurements on a disconnected device/source.

5th October 2015, 21:06

Hmm, that seems weird indeed.

I take it you have measure between the line, ref and the 0v line. Not just ground to the 3 pins.

6th October 2015, 21:00

Quote:

Originally Posted by MartinObviously

Hmm, that seems weird indeed.

I take it you have measure between the line, ref and the 0v line. Not just ground to the 3 pins.

Since voltage is difference in potential, I have tried both ways.
Between the battery - post and each of the pins I get 5V-3.6V-3.8V.
When I measure between the ref 5V and the "ground" I get 1.2V which is pretty much the same result. That is on every f*%$&(g sensor...

8th October 2015, 12:42

The PCM is fried. Since I'm unable to get my hands on a Bosch mp7.2, can I replace it with some other PCM, like Magneti Marelli and what would be the procedure?

9th October 2015, 09:57

What does the plug look like? Do you have a picture?

the 1.6 8v is the same as the VTR. If you find a single plug unlocked VTR ECU, that should work if I remember correctly.

9th October 2015, 11:19

Quote:

Originally Posted by MartinObviously

What does the plug look like? Do you have a picture?

the 1.6 8v is the same as the VTR. If you find a single plug unlocked VTR ECU, that should work if I remember correctly.

It's a single plug 3-rows of pins. It's a Bosch MP7.2 03 s.n. 9632693880 variant 4000.
Every ECU that I've found online is with 2 rows of pins but mine is 3, WTF?
Can you tell me is it posibble to use some other ECU (different sn. but same plug and design) without changing loom/sensors/BSI?

11th October 2015, 04:08

check the ecu tray... its most likely rubbed through the wiring loom and is shorting to ground

11th October 2015, 04:09

Quote:

Originally Posted by Mitnick

It's a single plug 3-rows of pins. It's a Bosch MP7.2 03 s.n. 9632693880 variant 4000.
Every ECU that I've found online is with 2 rows of pins but mine is 3, WTF?
Can you tell me is it posibble to use some other ECU (different sn. but same plug and design) without changing loom/sensors/BSI?

yours is 3 because its not a saxo.

same board different plug

11th October 2015, 19:18

Quote:

Originally Posted by blackie_2k5

yours is 3 because its not a saxo.

same board different plug

Some of the 106's are 3 row single plug. Maybe worth looking for an XS ECU?

11th October 2015, 20:13

Here is the thing... After ECU reset everything is fine (for a 20-30km) after that it starts going crazy. What I have noticed is after reset I have 2xbattery and 2xground on the stepper motor. After a while the become 4x4.5V. Pretty sad... The silver lining here is that I have found a great cliff with a pretty steep slope yesterday

.