307 hdi 136 recurring P2122 intake air heating solenoid

[tmead]

The car is a 307SW hdi 136, engine code RHR, on an 05 plate

This seems to be an intermittent fault, but has happened several times recently. It pops up an antipollution message, but reports on planet as P2122 permenant fault: intake air heating solenoid short to earth

Googleing reported a couple of pages where there is supposed to be a 'heater matrix' type thing under the air filter housing. I can't see anything like that, and there is no indication of coolant pipes heading that way at all. I'm inclined to discount this.

The full fault description page on planet (F6) shows:

ECU Fault code P2122
engine speed 1504rpm
measured injected flow 44.18mg/impulse
coolant temperature 81 degC
vehicle speed 84 kph
battery voltage 14.35V
engine status engine under load
time elapsed since ignition positive 572 s
bypass butterfly solenoid valve OCR 6%
EGR throttle electrovalve OCR 51%
measured airflow 360 mg/impulse
airflow setting 376 mg/impulse
intake air temperature at the air flow sensor -50 degC
inlet air temperature at manifold -50 degC

now I don't know about you, but the -50C seems a pretty odd reading to me, based in the UK in May/June ? live data shows a pretty normal value now, +37 I think, which seems fine quite a while after a short trip.

I'm not sure why both these values could be so wrong together - it does seem odd. I'm reluctant to head off to change the MAF on the offchance, but maybe will do the temp sensor because its cheaper ?

All help and suggestions about this issue welcome !

[Gibbo_Wirral]

Yep, the MAF does indeed measure the air temperature. But when its faulty it usually gives out a P code in the region P0101 - P0104.

Have you tried unplugging the electrical connector and reading the values or seeing how the car drives?

[tmead]

The car drives just fine, both before the error is logged and immediately after. no limp mode etc.

Live data from both temperature sensor and maf temperature are consistently in agreement.

I'm confused by the -50 C readouts, but the error is described as a solenoid short - could that be the solenoid that opens/closes the flap in the doser for the bypass ? They both measure 16.4 ohms. Does anyone have experience of the symptoms of solenoid valve failure ? Do they fail with an intermittent fault ?

Tim

[tmead]

Well, just maybe this is fixed ! There are two vacuum solenoids that live on a bracket above the starter, related to the 'air doser' that allows bypass of the intercooler (intake air heater ?) and these were held in place with a mess of tie-wraps when i got the car. The solenoids both measure fine for resistance with a meter, and the connectors are clean. A couple of months ago I took the whole lot out, including the bracket, and cleaned it all up. It was refitted with new nuts and washers on the mounting studs to hold the solenoids securely and prevent them rattling around. No issues since.

Now, was it the disconnection and reconnection ? Was it the securing properly to the bracket ? Was it dumb luck ? Will the fault recur now I've posted this ? Who knows !