Subject: C5 1.6 THP - "Gearbox Fault" + "ESP/ASR Fault" (Intermittent issue, no permanent codes)

[behery]

Good afternoon everyone,
I'm facing an annoying intermittent issue on my 2013 Citroën C5 X7 (1.6 THP Petrol, Automatic gearbox Aisin), and I could really use your expert advice.
A couple of weeks ago, my car started randomly throwing the "Gearbox Fault" error message, immediately followed by "ESP/ASR System Faulty" and the Service light. When this happens while driving, the gearbox goes into (locks up in 3rrd gear), with S & * flashes .
However, if I pull over, turn off the engine, disconnect the battery for seconds, then connect again and turn on the engine, both faults completely disappear, and the car drives smoothly again as if nothing happened. These issues started occurring more frequently recently (about 1–2 times a day).
The main diagnostic challenge:
When we run a diagnostic scan (Diagbox) while the car is running normally, we don't see any active or permanent fault codes pointing directly to the root cause—it's completely clean until it happens again on the road.
When we scanned while the errors occurs we got this codes

P1605
U1208
P0072
U1218
U1113
P0072

Has anyone here experienced this exact combination on a 1.6 THP model?
Any suggestions or guidance would be greatly appreciated. Thanks in advance!

[Paul-R]

Can you put the descriptions to go with the error codes please?

[behery]

Can you put the descriptions to go with the error codes please?

Yes
Here are the codes:
First: Transmission Control Module (BVA_AM6_AT6_EURO5 FAULT READING)
U1208: Signal error transmitted by the engine management ECU over the CAN network 
U1218: Fault in the outside air temperature received on the CAN network 
U1208: Signal error transmitted by the engine management ECU over the CAN network 
P1605: Engine torque required by the driver information not received by the CAN fault (Engine ECU) 
Second: Engine Control Module FAULT READING)
P0072: External air temperature information 
U1218: CAN 
P0070: External air temperature information 
P0030: Upstream oxygen sensor heating command 
U1113: CAN 
P0947: Oil pressure regulation solenoid valve control

[lcwin]

check your battery, if its not in good condition the ECU will throw random fault codes. Check the alternator as well as it tend to fail often since it sits near the exhaust.

[behery]

check your battery, if its not in good condition the ECU will throw random fault codes. Check the alternator as well as it tend to fail often since it sits near the exhaust.

"When this issue first started, I immediately replaced the battery. The problems disappeared for about two weeks, and then they started appearing again. Yesterday, we tested the alternator right after starting the car with the loads on, and it read around 13.8V. Could it be that the alternator weakens after driving the car for a good distance?"

[mickthemaverick]

You could get a cheap voltmeter like the one in the first link, connect it across the battery and run wires into the cabin, and then monitor the voltage while you are driving to give you an idea of the alternator's performance. You can get ones that plug into the aux socket but that may have a regulated supply so wouldn't tell you the alternator's output voltage. One such example in the second link below:

https://www.ebay.co.uk/itm/366633649266

https://www.ebay.co.uk/itm/227344424212

[behery]

You could get a cheap voltmeter like the one in the first link, connect it across the battery and run wires into the cabin, and then monitor the voltage while you are driving to give you an idea of the alternator's performance. You can get ones that plug into the aux socket but that may have a regulated supply so wouldn't tell you the alternator's output voltage. One such example in the second link below:

https://www.ebay.co.uk/itm/366633649266

https://www.ebay.co.uk/itm/227344424212

That's a great idea! I will connect it to Diagbox tool and monitor the live data while driving to see exactly what the alternator is doing.

[behery]

You could get a cheap voltmeter like the one in the first link, connect it across the battery and run wires into the cabin, and then monitor the voltage while you are driving to give you an idea of the alternator's performance. You can get ones that plug into the aux socket but that may have a regulated supply so wouldn't tell you the alternator's output voltage. One such example in the second link below:

https://www.ebay.co.uk/itm/366633649266

https://www.ebay.co.uk/itm/227344424212

I have a quick question: why doesn't the ECU trigger a direct, explicit fault code indicating that the alternator or battery is failing?

[mickthemaverick]

A good question but one that is beyond my knowledge!!

[behery]

check your battery, if its not in good condition the ECU will throw random fault codes. Check the alternator as well as it tend to fail often since it sits near the exhaust.

I completely replaced the alternator, and checked the grounds, but the exact same issue is still happening. By the way, the battery reads 12V and the alternator reads 14V."