polo 1.2 AWY O2 sensor 2 P0036 code

[shep73]

Hi all

53 plate polo 1.2 AWY 63K miles

looking for some advice regarding the downstream 02 sensor. I'm getting the error code P0036 - H02S heater control circuit bank 1 sensor 2. After some research would seem that the O2 sensor is not heating up. I've disconnected the manky multiplug, cleaned off 12 years of corrosion/dirt and I'm able to get 12 volts from the engine loom side with the engine running. Seems to point towards the sensor being gubbed.

so do i go for a eurocarparts special HAAS for £28 or do I get a Bosch or NGK one for more cash ? I'm pointing towards the more expensive one as been caught out in the past with the old buy cheap buy twice adage, if anyone has any experience with the HAAS one I'd be glad to hear it

any advice greatly appreciated

Brian

[niall campbell]

has to be Bosch or NGK


if you register online & order the carparts before you drive to EuroCarParts, get free delivery etc then they will send out a 30% discount code in your email account

[Crasher]

http://www.eurocarparts.com/search/710770407

[shep73]

Thanks for the replies niall and Crasher

NGK sensor on the way

next job non working engine fan :zx11: thought I had cracked it with replacing a fuse on top of the battery box, but that would be too easy....

Brian

[Crasher]

The fans burn out inside, we do lots.

[shep73]

Going to have a look at it later Crasher, check to see if it powers up with a direct power supply and so on.

If it is knackered (sounds likely) where is best to get a new one ?

Brian

[Crasher]

PM me the cars reg

[Crasher]

2004 model fan number 6Q0 959 455 AF which is £188.28 from VW

ECP do a reasonable EIS Cooling Fan (http://www.eurocarparts.com/search/213440900) and an original Valeo Cooling Fan (http://www.eurocarparts.com/search/213440905) which is what I would fit to a customer’s car for peace of mind.

[shep73]

Thanks Crasher

hopefully get some time to investigate a bit more over the weekend

Brian

[shep73]

wee update

finally managed to get a bit of time to replace the 02 sensor - one job done !

checked the fan by jumping the switch power supply and that worked, so immediately blamed it on the fan switch. Stuck a new one on and gave the car a good clean while waiting for the temperature to come up and yes you guessed right - no result. had a poke around underneath and the bottom radiator hose is stone cold ! yipee a new thermostat added to the shopping list. I was sure when i fitted the new front end and radiator it was warming up ok, but I am restoring a 944 with a non working radiator fan so may have mixed them up

322553225632257

some precision engineering (chassis leg realigned with big persuader!) new bumper bar/front end housing including radiator from U pull it, bumper (wrong colour so first attempt at spray painting)
and back on the road properly for £40 !

The guy I bought it off had a dodgy back street repair, involving the bumper reinforcement bar cut in the middle to aid using wood screws to reattach the bumper and some of the front end, nasty stuff and rather dangerous.

Brian

[shep73]

Having read over the above post and consulted the mighty Haynes manual of all knowledge, I am a bit stumped

Top hose hot, so thermostat opening. Doesn't appear to be an air lock, feels like there is coolant in the bottom hose. Waterpump ??. I dont remember if I opened the vents to warm while bleeding the system - cabin gets nice and hot though. At the MOT the tester said the engine was a little bit hot while testing the emissions...... I hoped that was just the fan not kicking in. Would seem the coolant is not circulating so again points to waterpump. Flushed the whole system before putting it back together and filling up

Help !

Brian

[Crasher]

If the heater is hot the water pump may be OK but they are easy to pop off and take a look.

[shep73]

looks pretty straightforward, going to give it a try tomorrow

what else would it be?

Brian

[Crasher]

Did you replace the thermostat insert or the complete unit?

[shep73]

I was just going to replace the insert, but looking at other posts it would seem prudent to replace the whole thing, seems pricey for a little bit of plastic!

Are my symptoms the right way round for thermostat failure ? the Haynes manual says its open/ working if the top radiator hose is hot. I was going to have a look at the whole system again and check for an air lock first before I spend any more money.

Brian

[Crasher]

Replace the complete unit, VW part number 03C 121 111 B but these are £151.75 from VW, this Topran Thermostat Housing (http://www.eurocarparts.com/search/209440560) is lower priced BUT over the last 35 years Topran parts have not been great for me, going aftermarket a Meyle 128 228 0005 would be my choice.

[shep73]

Thanks for the heads up Crasher, your advice is much appreciated. I've used Meyle parts on my 944 and they have always been good quality, so have ordered a complete Meyle housing and thermostat. Im pretty sure its this, as the housing and bottom hoses are stone cold when the engine is up to temperature, the thermostat closed circuit including the supply to the heater matrix warms up fine.

Thanks again

Brian

[Crasher]

They are an interesting company, they were not an OE supplier until Morgan partnered up with them recently, I have used lots of their parts. The UK operation is part of VW Heritage so it's enthusiast owned. My only problem is getting stuff from them, local my dealer is Parkers and they always seem irritated when I order something.

[shep73]

So, after replacing the thermostat and housing its still the same!! hoses from the thermostat down to the bottom of the radiator stay stone cold. Either the new thermostat is gubbed or the water pump isn't working effectively.

grrr, was pretty sure the new thermostat would have fixed it

looks like a look at the water pump is in order

Brian

[Crasher]

I have never had one of those 3 cylinder pumps stop pumping, leak yes. At least they are easy to do.

[Rob69]

Is it not just the radiator working well enough with an idling engine without the fan in the current low ambient temperatures, preventing the coolant at the fan sensor (located at the cool bottom of the rad) getting hot enough to switch it on ? If your heater is working ok and the engine is not overheating while driving then i'd think the WP is ok. Can you drive it hard up a long steep hill to get sustained high load on the engine, then pull over at the top and have a look and feel at the hoses. Even consider blanking the rad with cardboard during this test to prevent air flow, but being carefull not to cook it!. Have you got an OBD tool you can plug in to get a better idea of coolant temp at the CTS. I've recently had overcooling issue on my passat and used vcds and a obd scanner to get better temp indication than the dashboard temp gauge.

[shep73]

Thats a good point, will try that on the run home from work tomorrow. My local indie commented that the car was overheating when doing the emissions testing for its last MOT, but since it only ever does short journeys I've never really bothered to look into it until now.

Thanks for the advice guys

Brian

[Crasher]

The reading on all modern VAG cars temperature gauges is meaningless, dangerously so. It reads 90 at a real 77 and still reads 90 at a real 117!

[Rob69]

Exactly, I think even a lot of basic OBDII diagnostic tools can give a CTS readout to get a better idea of true temperature.
The reading on all modern VAG cars temperature gauges is meaningless, dangerously so. It reads 90 at a real 77 and still reads 90 at a real 117!

[shep73]

gave it a good thrashing on the way home ! nice and warm by the time I'd made it up the bigger of two hills. Thermostat housing and lower radiator hose stone cold !!!
Pretty sure its still a thermostat problem. Going to pull the new one off and check it opens properly