C5 2012 - P0928 Error

[Karolis Vansevicius]

Citroen C5 III 2012 2.2HDI 150KW Automatic
Hello,

A month ago, I purchased this citroen. Now it started to show "hidden" problems.
After longer time (minimum 4hours), when I turn ignition - it gives me a gearbox fault message with code P0928. And I couldn't change the gears. Repair shops couldn't diagnose the problem.
What has been done?
1. Changed the battery
2. Changed gearshifting mechanism (I don't know how to call it.)
3. Changed Relay which is responsible for gearshifting. (Behind the pedals)

The strange thing, that if I clear that code using diagnostic tool, I can start to drive and there's no problems at all, everything works perfectly. The problem starts to appear again only after a few hours when the car is locked. If I try to start it again after about 30 mins - everything is ok, but if I try to start it after 2 or more hours - problem appears.
Maybe you have any ideas?

[GiveMeABreak]

Pop your VIN up so I can see exactly what you have. Please post your VIN in full without spaces - it will be automatically masked from public view after submitting your post & will only be visible to staff.

[Karolis Vansevicius]

VF7**************[VIN obfuscated, can be read by forum staff]

[GiveMeABreak]

Ok, so this is a shift lock problem. P0928: Fault on the lever locking actuator circuit (shift-lock): Short circuit to positive.

Fault Code:	P0928
Description of Fault:	Fault on the lever locking actuator circuit (shift-lock) : Open circuit or short circuit to earth. Detection of a voltage of 0 V for 0,5 seconds on the shift lock solenoid. The time of appearance of the fault code is 1s Context of appearance of the fault code The following conditions have to be met - Ignition switched on - No COMELEC ECU (*) Technical precision on the context of appearance of the fault code: The following conditions have to be met: - The system should not be in down-grade mode - Battery voltage between 10,2 and 15,5 V - No fault codes found : U1003 - U1108
Conditions for Fault to clear:	No locking of the lever in P
Downgrade Modes whilst Fault is active:	"SERVICE" warning lamp Sport warning lamp - Snow warning lamp Automatic or 6-speed piloted manual gearbox warning lamps (Orange PRND triangle) Display of a "-" on the fascia panel
Symptoms:	Difficult/impossible to change gear
Suspect Areas:	Shift lock solenoid Engine compartment main electrical harness Automatic transmission control unit

When you can't move from 'P', you need to do the following in order to unlock it temporarily:

Releasing the "shift-lock" (with an operating anomaly)
Impossible to release the "shift-lock" following the usual procedure.

Probable causes of the anomaly

• The causes of malfunction can arise from the following elements :
• The battery voltage
• The "shift lock"
• The selector lever position switch
• The automatic gearbox ECU
• The wiring harness

Operations to be performed

Unclip and move aside: The bezel (1).

Unlock the "shift lock" with the aid of a screwdriver - Press on (2) (In the direction of the arrow ).
Move the selector lever to disengage it from the "P" position.

[Karolis Vansevicius]

I think if its a physical problem, clearing the error would not help. But I clear it and it appears only when car is locked for a few hours.

[GiveMeABreak]

It means it's likely to be an intermittent fault, so the fault code will keep coming back - so needs attention as you don't want to be manually releasing it all the time. Looks like the solenoid or the supply, so it's not releasing all the time.

[Karolis Vansevicius]

Ok, strange. Today I tried to put in the key and wait for 5 secs. Then start ignition. And I get 0 errors.

[Karolis Vansevicius]

Nope, just tried again. The same issue.

[GiveMeABreak]

I've already listed the probable causes and suspect areas above. Clearing a fault code is not going to make any difference if the underlying issue is not fixed - it will just keep coming back. It needs investigation to determine the actual cause using the information above to help you.

[Karolis Vansevicius]

Yes, I read that info on Google. I need advises from people who experienced this problem, because it can relate to the other malfunctions

[GiveMeABreak]

Well if you want to put your faith in 'Google' go ahead, but this is the technical reason for the fault and this is the official explanation. And you're welcome by the way....

[Karolis Vansevicius]

Ok, so where I should search for a problem if everything is ok until I leave a car locked for more than 4 hours?

[GiveMeABreak]

Well battery voltage for one - 4 hours means most of the the ECUs have gone to sleep, except the active ones that detect the unlocking request, TPMS monitoring, Alarm as examples which all put a drain on the battery. How old is the battery? Anything over 5 years old is probably toward end of service life it it's not holding as much charge.

As per the fault code diagnosis table I put up, the solenoid is not getting power for at least 0.5 second, which could be the solenoid or the power to it / wiring. So all these can be a possible reason and therefore each person's vehicle may have a different cause. You now know how to unlock it when this happens and have some pointers for further investigation.

If you don't trust your local garage to fix it, just get the dealer to sort it - they will have the correct equipment to test and diagnose the problem, that may be cheaper in the long run.

[Karolis Vansevicius]

Battery is ok, just replaced with a new one.
Relay responsible for gears - replaced
Gearshifting mechanism - replaced.

One moment, I didn't mentioned - local garage found that my gearbox ecu connected directly to battery.. I don't know reasons for that.

[GiveMeABreak]

Well that's not right for a start and potentially harmful. The Gearbox ECU should be connected to the passenger compartment fuse box via wire BH16C (at gearbox ECU end) to B163 (at Cabin Fusebox end) to fuse (G36).

Also maybe worth checking your brake twin switch.

1603 : assembly (automatic gearbox control)
1630 : automatic gearbox ECU /
1642 : gear lever blocking actuator control relay
2120 : brake twin function switch /




Wire 6742C is the shift lock command.
Wire C161: ignition controlled +ve (To Engine Fusebox PSF1, fuse F7)