Citroën C2 VTS 1.6 16V – Backfire at 7000 RPM and Limp Mode

[Nikola vts]

Hello everyone,

I have a Citroën C2 VTS 1.6 16V and I’m having a strange problem.

When the engine reaches around 7000 RPM, the car backfires from the exhaust, the SERV light comes on, and the car goes into limp/safe mode (it won’t rev above about 3000 RPM).

It also happens sometimes under heavy acceleration. For example, when I accelerate hard in 2nd or 4th gear around 5000–6000 RPM, the SERV light comes on and sometimes the car goes into limp mode, and sometimes it just loses power but does not enter limp mode.

After I turn the car off and start it again, everything goes back to normal. After driving for about 100 meters, the SERV light usually disappears.

The car drives normally during light driving, but the problem appears when the engine is under high load or high RPM.

Has anyone experienced a similar issue with the C2 VTS or the 1.6 16V TU5 engine?

Any help or suggestions would be appreciated.

[mickthemaverick]

I'd suggest you have a diagnostic to see what fault codes are stored and then decide what to do next.

[Nikola vts]

I have these codes:

P0141 – Downstream Oxygen Sensor Heater Control Circuit – Permanent Fault

P0121 – Throttle Position Sensor / Switch A Circuit Range/Performance (Signal Inconsistency between Signal 1 and 2) – Permanent Fault

[ozvtr]

When the engine reaches around 7000 RPM, the car backfires from the exhaust,
when I accelerate hard in 2nd or 4th gear around 5000–6000 RPM, the SERV light comes on and sometimes the car goes into limp mode

I take it that this is a second hand car? Do you know the history of the car? How long have you had the car? How many miles on the car?

Someone would not buy a brand new VTS to go shopping, or to take nan to church on Sunday! So my guess is that it's already been flogged and your not really helping matters.

Ok so let's be constructive then.
The TU5 was designed to run the plastic inlet manifold and plenum. So when they put in a whacking great lump of aluminium for the inlet manifold, it had problems with the manifold working loose. This caused vacuum leaks. I don't think that's your problem here, but you could still check it.
I might point the finger at carbon build up. What's the oil consumption like?
I don't know why the engine goes into limp mode after the back fire. It can only detect misfires and that wont send it into limp mode.
Back firing into the exhaust is typically from a rich air fuel mixture. Not all of the fuel gets burnt and then ignites when it hits the hot exhaust system. A leak in the exhaust manifold will do two things. Cause the oxy sensor to think the air fuel ratio is too lean, causing the engine ECU to richen up the mixture. Second, it will add more oxygen to the rich mixture coming out of the exhaust ports. So you could check the exhaust manifold for leaks or cracks.

I have these codes:

P0141 – Downstream Oxygen Sensor Heater Control Circuit – Permanent Fault

P0121 – Throttle Position Sensor / Switch A Circuit Range/Performance (Signal Inconsistency between Signal 1 and 2) – Permanent Fault

The P0141 will not cause any change in performance of the engine. It will cause the engine light to come on however.
The P0121 WILL cause the engine to go into limp mode. The code is self explanatory. It's a "fail safe" of the drive by wire system.

On the surface, only having this information, I can only assume that the back fire is causing the P0121!!! A backfire, by itself, wont cause limp mode. However after a backfire event, the car goes into limp mode and you get the P0121?