Fiesta Engine management light

[Silvery Moon]

I'm working on my brother's 54 plate Fiesta 1.4 petrol. The Engine Management Light is on. There are two codes stored, P0030 "H02S Heater control circuit bank 1 sensor 1" and P0036 "H02S Heater control circuit bank 1 sensor 2" As I understand it, the lambda sensors have a heater built in to them and on the Fiesta this is supplied from fuse 13. I've checked the fuse and it's OK. I think it unlikely that both sensors have failed and I'm looking for suggestions on other checks I could carry out before replacing the sensors. Anybody got any ideas?

[Deleted]

If the fuse is good then the fault is either:


a) the wiring

b) the sensor(s)

c) the sensor(s) are not compatible with the software in the engine ECU (if a genuine Ford part you can discount this)

d) the engine ECU has a fault (unlikely)

[valhalla]

How quickly do the codes come back if you clear them down?

The sensors are fed by a common power supply, and one thought is to try unplugging each sensor, one at a time, and see which one allows the other sensor to work; my thoughts are that the heater circuit on one is dragging the other down. Obviously, other faults will crop-up as you unplug each sensor, but if you can isolate which sensor is still working on the heater (the one that works when the other is unplugged) then that might help.

[Silvery Moon]

"How quickly do the codes come back if you clear them down?"

If I clear the codes then run the engine the light stays off until I shut it down. Then, when I restart the engine the EML stays on and the codes are back again. Tomorrow, time permitting, I'll try unplugging the sensors in turn as you suggest and see what happens.

[givusaclue]

check all the fuses first
valhalla is almost certainly correct (usually is  ) regarding common supply & i think i've had a fiesta in the past with that fault which was a blown fuse

if it is, then you may need to check out why the fuse has blown however