Another emissions service error (but stops car)

[basherX]

2010 4.7 V8 manual

I have an annoying variant of the emissions service error. Annoying in the sense that when it occurs it cuts the engine, it’s sporadic and despite having narrowed down the triggering scenario I can’t replicate it at will.

Very occasionally as I approach a junction/queue/lights etc I’ll depress the clutch, whilst still in gear and after (say) 5 seconds of coasting or so the engine stops, display indicates an urgent emissions service warning along with a red triangle.

To start with I thought it was just a stall but I’m now certain that it’s not.

Always that scenario or a minor variation thereof. Never under load.

Car restarts immediately and substitutes the error with a yellow triangle and the typical emissions service warning. Car runs fine with those.

Has been to DAE when I first had the fault but couldn’t best explain the circumstances (because I hadn’t twigged the coasting pattern, above) and nothing stood out as obviously wrong.

4 Error codes are:





Note: the PCM/Immobilizer fault is a new one to me: when I’ve had this issue previously I haven’t seen that fault. It may be unconnected- I’m just back from 2k miles round Scotland so maybe more than one issue is manifesting (?) or it may be related. Not sure.

The odd thing (to me) is that the other three codes are all throttle related- I’m 99% sure that there’s no throttle input at all in the scenario when the fault arises.

I’ll raise (again) at service in August but interested whether the hive mind has any particular thoughts about what the root cause may be.

[XMark]

Without reading live voltages etc, that screams throttle body to me, good luck bud, I feel your pain

[skhannes]

This screams TPS to me. I'm not sure if the TPS can be replaced separately from the TB

What P1579 is saying is that when throttle demands some value (let's say 30%), the TPS loses signal at that point. Therefore, the system generates P2104 which forces the TB blade to an idle (safety percentage of the throttle blade)

With a drive by wire system, it is critical the signal the throttle pedal sends (gas pedal, throttle demand) is picked up by the TPS and matches the same % as throttle is demanded. If not, a drive by wire system is always going to default to a safety position (such as idle) as the alternative could kill someone. This is also reflected in the P2111

I see no nexus with the P1259. You have to be careful with P codes in the 1250 to 1260 range as Aston defines those differently than how many manufacturers use them. On the latest platform for example, a P1260 means an interruption in the pathway from the IAT to the ECU where the rest of the world defines a P1260 as a vehicle imobilizer event triggered BC of a theft event.

[basherX]

Thank you gents- really helpful.

And Steve, that explanation sequence makes sense: loses signal on throttle position (fault), forces idle (fault) and because it’s now set at idle this then faults again because the throttle is fixed in one position. Thinking about it, it may be me trying to engage the clutch (into 1st whilst ending the coast) that finally stalls the car and triggers that final fault code.

Definitely gives me something to work with.

[stevenichols]

You could try cleaning the throttle body - very easy to do. Also, see my posting about "emission service required." I thought it was the O2 sensors, but after taking the right hand wheel arch liner off I found that the air inlet pipe had come away from the pipe to the throttle body. Fixed that, cleaned the MAF sensor and it is running like a peach now and no more errors.

[basherX]

Thanks. A few things to try. Although the throttle body itself is spotless which makes me wonder if the previous owner was in there before me.