Can I ask for some advice, my wife's car is a MK3 2006 1.8 38K miles and due to family life getting in the way of having roof down fun this year the car has seen very few miles put on it which is a shame and its being stored dry in the garage and occasionally has to be moved out of the garage if I need access to work in the garage, it is either usually started and stopped straightaway or left to idle up to temperature until fans kick in, car has only been driven to a few local car shows.
I usually do keep the battery up to full charge but it has been a few weeks since the car was last started, all fluid levels are correct and is looked after even while not being used.
However today when I went to start it the engine just about started due to the battery voltage being a bit low and immediately the engine management light was illuminated with engine running. I connected my code reader and it read,
P0031, which I believe is HO2S Heater Control Circuit Low Bank 1 Sensor 1.
Now I will admit I am not that technically minded when it comes to these sort of things, have never had an engine management light problem on any of my cars before.
Thinking it may have been something to do with the battery charge being low I switched the light off with the code reader and left the car to idle for some time but eventually the light came back on again, engine now starts fine now battery has more charge, I then disconnected and charged battery further for several hours then when the engine was cold reconnected, with ignition on checked all fuses in both fuse boxes that had power going to and from them and all appear ok, 14v at battery terminals on idle, on start up the light stays off but comes on again once engine warms up a bit.
Haven't yet had a chance to physically check the sensor or wiring, could it be the sensor is fouled up a bit from not being driven and can these sensors be taken out & cleaned?
Won't be using the car over winter so have time to sort out this issue, I did use the search function on the forum but most posts relate to mk2 cars.
because the car hadn’t been driven much and not always run up to full temperature would this be a contributing factor why this sensor may have failed or is it just one of things that fail at random?
Just thought I would ask about cleaning it since it hasnt had proper drive. My original thoughts to why light was on was because battery voltage may have been a bit low on start up and being only start stopped for the last few months causing sensor to get fowled up.
So if it needs a replacement sensor which brand to buy and which to avoid? I done a search earlier on Miata.net and there was a comment saying the Mazda sensors are made by Denso, should I try a source one of these?
i have a sensor socket ordered but will do the prep work maybe tomorrow, will look into the plusgas, have similiar sprays here one of which my dad used to use for removing stubborn bolts on trains, rustflash think its called, wd40 and some other 40+ spray.
Never having changed one of these before is it ok or advised to put some copper grease on the threads on reassembly?
So this morning I made a start into tracking down the fault, removed the heat shields from around exhaust manifold without too much trouble and checked condition of wiring on sensor which looks ok, removed front wheel to improve access to wiring connector, removed and checked wiring connector it actually came apart a bit easier than I was expecting which made me think it might not have been pushed all the way home, pins inside connector look fresh with no signs of corrosion or water ingress, refitted connectors with a positive click so I know it's fully home, I cleared codes & restarted engine and ran up to temperature with no signs of light coming on unfortunately after a few restarts light came back on again with the same code P0031.
Before I attempt to unscrew the sensor with the wiring unplugged it is long enough for easy access for testing , how do I test the sensor and what figures should I be seeing.
As I said in my first post have never had any experience in having to do these types of repairs so I am learning as I try to fix the fault.
I have some experience of lambda sensors and associated exhaust systems.
will spend a bit of time trying tracking down a cheap replacement and PM you later.
The main issue here is getting the old sensor out without damage to the manifold lambda boss threads. Take Eddie(Drumtochty’s) advice for the best chance of clean removal. I understand you are going to use a specific Lambda socket - good move.
When refitting the new lambda, it should be supplied with anti-seize grease on the threads, so future removal perhaps less of a problem than it might be. Given the likely mileage and age of car I seriously doubt this will be an issue for you.
When mine packed up, same error code as you have, I chickened out of doing it myself as so many people told me how difficult they can be to remove. I have a trusted garage and let them do it. They charged £150 for the sensor and a half hours labour to fit it. I think the sensor is a Denso but couldn’t say for sure.
Many thanks for your help, greatly appreciated, I don’t mind spending money on a brand that is a bit more expensive if it’s more reliable, from what I can gather a genuine Mazda one is around £400, can’t afford that, was also told it’s a Denso part but not sure on this.
well it’s a lesson for me on how these sensors work.
Quick note regarding upstream sensor removal and fitting :
When replacing the exhaust manifold on my Mk3.5 last month I was very vigilant about nit damaging the sensor so attempted to unscrew it while the manifold was still bolted to the head to avoid it being knocked when maneuvering out the manifold. To my astonishment the sensor was only hand tight! This car was oem with full mazda service history and no mention of work being done on the sensor.
Also the new sensor will probably have anti seize already applied to the thread with a little removable sleeve and a leaflet saying don’t get any of it on the sensor itself.
Quick update, have new sensor, socket for sensor, lots of spray oil and can’t get the old one to slacken, have tried with engine hot and engine cold, cut wires on old sensor and used a deep socket with half inch drive breaker bar and still nothing, I have a truck mechanic friend who is gong to call and have a look and will see what happens.
Have other things in life to concentrate on at the moment so bonnet will be left closed over the weekend.
We managed to get old sensor out eventually, threads where ok just was very tight, new sensor fitted with some copper grease on threads, cleared codes, and all now seems good now.