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For future info to members and guests I thought I'd record the problems and fixes I've just made to my daughters Peugeot 207. Very frustrating to pin down but sorted in the end. May also be applicable to other marques/models with similar engines or ECU design e.g. Citroen C2

a) Actual fault code P0336 re-occurring weeks apart b) Spurious fault codes for conditions that don't exist, c) annoying unnecessary seatbelt warnings, d) not showing fault codes when engine occasionally refuses to start or refuses to run above idle, e) going to limp mode for no apparent reason, f) On three occasions un-drivable.

a) A genuine problem. Fix: A new crankshaft sensor can be purchased for less than £15 from various sources. Located just above and to the right of the oil filter housing (viewed looking down under the bonnet). Only need a 10mm ring spanner (to remove one bolt) and takes less than 15 minutes to remove old/fit new one.

b) to f) All caused (in my case) by a known, but not well documented problem - Water in the base of an ECU plug. In this example the water was in the front (of the 3) connectors. Deep enough to cover most of the pins, corrosion had started at 2 of the pins (indicated by a green colour deposit). Fix: Lift off plastic covers from battery (this exposes the ECU connectors). Remove the zip tie from each connector (if still fitted). Open the lever of each connector (which disengages the plugs). Carefully remove any water found (I used kitchen roll tissue). Spray affected parts with electrical contact cleaner only (I used some Holts I had from Eurocarparts). Taking care not to bend any pins, gently clean away any deposits (I was miles from home so used a hairclip with some tissue and electrical spray). After ensuring all cleaner has evaporated and no tissue debris left in the male/female connector parts, refit the plugs (can't mix them up). Re-fit the battery covers (back one first, then front one). Restart car - in my case all fixed.

Some folks have put this down to water leaking from the temperature sensor in the thermostat housing. In my IMHO this is unlikely (and in my case definitely not). I suspect repeated condensation events, but we'll probably never know :)
I wouldn't recommend using anything else but electrical contact cleaner and certainly not use any coarse abrasive products. If pins are badly corroded/weakened you may need to fit a replacement ECU. Should you get stuck away from home, just try drying the part(s) out first and see if that gets you going and back to base.
The above procedure is obviously not a cure all, but would cost little to nothing to check and eliminate should you have similar problems. Good luck!

7,836 Posts
Glad you fixed it.

Washer pump can also allow water to track up wire into fusebox.

Both the faults are well documented with official service fixes and a modified harness on later versions.

I had coolant in the daughters ecu. When I replaced the sensor (and ecu) I cut the cables put some heat shrink on soldered them back together and then shrunk only one side of the heat shrink to keep it in place and stop any chance of it happening again

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