Lord Iffy Boatrace

Yep cleared the old codes. It’s the same fault appearing when it does appear. The rear sensor is on the list next if it starts to become a bigger problem again. Having just spent 1200 quid on new tyres, the sensor, mot, service and tax though and with insurance due in a few weeks I’ll wait a bit :)

Oh and it's just passed an MOT and exhaust emissions check with no problem.

OK just to update this in case someone else finds it useful. Garage did a thorough check for vacuum leaks. There were none. So I bit the bullet, and ordered the proper Toyota fuel/air ratio sensor from Amayama. Fitted this. Problem is not entirely solved now, but instead of the light coming on and the code being reported immediately, I can drive for hours at a time and days will go by before the light comes on. Once it comes on, it won't turn off until the engine is turned off, but then you can start the engine and it won't come on for a long while again. The fuel economy returned to what were the levels before the problem started. I've since replaced the spark plugs (pretty sure these hadn't been done since it was imported 3 or 4 years ago) and the old ones were carboned up as expected due to the mix being too rich. Also replaced the air filter as part of a service. Still the same. One thing appears to be certain - the cheap aftermarket air/fuel ration sensor does NOT function correctly in my Alphard. Replacing with genuine Toyota part was the way to go. So at this point, I'm going to live with it unless it gets worse again, on the basis that "if it's (not too) broke, don't fix it".....

OK more digging around produced this: https://www.autoequipment.com.au/image/data/Support/Toyota%20Planar%20Sensors%20-%20Part%203.pdf Which appears to be the specs for the upstream O2 sensor used in these engines (more correctly called an air/fuel ratio sensor I have learned). It seems there are two versions, a "cup type" and a Planar sensor (the cup type being an older design). The resistance specs for the cup type are 0.8 to 1.4, but for the planar type it's 1.8 to 3.4 ohms. I've confirmed that my alphard uses the the Planar type, and also I re-measured as the engine was a little warm earlier and the new sensor I put in measures 2.8 Ohms so is within spec. So scratch that theory! Also checked the voltages on the wiring loom connector and there's 12 volts getting to the heating part of the sensor, and I'm getting 3.3 volts on one sensor pin and 2.9 on the other, and 12 volts on one of the heater pins and ground on the other, which appears to be correct. At this point I'm back to either some sort of vacuum leak, or something broken that's unconnected to the sensor. Unfortunately my scanner (an Ancel JP700) only lets me read and erase fault codes on the Alphard, it's datastream OBD2 function doesn't work, so I can't see what the sensors are reporting to the ECU when the engine is running. I'm probably going to have to quote Clint Eastwood at this point and declare "a man's gotta know his limitations" and take it somewhere that can do a proper vacuum leak test and get the full diagnostic data from the ECU.

OK so 2 days ago I checked the sensor - removed it and put it in again, it was fine, not cross threaded or anything like that. I also gave the connector on the car side a good spray with electrical contact cleaner. Since then the fuel consumption seems to be better, but still getting the engine light. This morning I checked the codes with the scanner and now have got a P0031 error as well as a P0171. Going down a google rabbit hole, I got the multimeter out and checked the resistance across the black wires on the sensor side of the connector, which reads 3.2 Ohms. The old sensor I took out reads 2.7 Ohms. I can't seem to find a definitive spec for what the sensor reads, but again google is saying that the Alphard's ECU (2AZ-FE engine) is expecting the resistance to be 0.8 and 1.4 Ohms at 20 degrees Celsius. The sensor I put in was a cheap aftermarket one (branded "BIVVI") form Amazon, I was too tight to buy the real thing from Amayama! So am wondering if me cheaping out might be the problem here. Does anyone know for sure what the spec on the sensor needs to be? Suspect that the one I replaced was bad, and the new one is just not manufactured to the correct tolerance needed by the Alphard.

Thank you! Yes I replaced the top one (bank one). I could try and replace the one you've shown I guess, but apparently that would be more of a P0174 code, and I've read that it only monitors the post-cat exhaust gases and doesn't affect the fuel mix. Might give it a go anyway. Thanks for the tips, I will check the O2 sensor I replaced is fully seated.

So started getting a P0171 fault on my 2006 2.4 Alphard in August 2025. To try and solve it; 1) Replaced EVAP charcoal canister (it was knackered and leaking so replaced it) 2) Replaced PCV valve (fuel consumption got way better after this, went from about 280 miles per tank to about 320) This was in August 25. Engine Light was still coming on after driving for a while (30 minutes or so) and the Ancel JP700 scanner showing P0171, but fuel consumption was so much better and had other things to do so left it. In the last 6 weeks though I picked this up again: 3) Replaced MAF sensor 4) Ran cat cleaner through the system Same symptoms. So I then 5) Replaced upstream O2 sensor This is where it changed. I reset the ECU, and then drove around for 45 minutes while it relearned. It went through the stage of sorting out the idle (was too low for a few minutes before sorting itself out) and it ran "lumpy" for a short while, but by the end of 45 minutes or so it was running excellently, and no engine light and no fault code on the scanner. Excellent I thought! However.....next day, I started her up and although it ran fine, the light came on after about a minute, and sure enough, P0171 is back. Since then, (a couple of weeks ago), every time we drive it, same thing happens, and the fuel consumption is now terrible - we're lucky if we're getting 180 miles per tank! Clearly the ECU is injecting far too much fuel because it believes the engine is too lean, and since replacing the O2 sensor this has got worse. My guess is that the previous sensor was faulty and wasn't reporting as much O2 in the mix as the new one is? Or because I'd reset the ECU, it's now learned differently and wants to stick more fuel in. Air filter is fine, was new at July 25 looks clean. Was last serviced in July 25, oil changed. What's next? It was checked for vacuum leaks when the EVAP canister was replaced, but I guess I should get it checked again (and for exhaust leaks) in case that's causing an issue. Maybe the new sensor is bad? But that doesn't make a lot of sense as the old one was present also for this fault code. Is it time to move onto fuel pump and filter? What else could be going on? Google says outside of all this then could be an knackered cat, or ECU itself damaged, or possibly injectors.....anyone got any ideas on what's most likely?

So had the parts fitted. Still got the engine light! However my fuel consumption is WAAAY better so there's that! Back to drawing board on fault PO171.....

Happened to me last year. Sheathing on the cable had disintegrated and cabled had got wrapped around door mech. Had to get whole power door motor mechanism replaced. Cost about 400 quid int total as I recall.

Parts turned up from Amayama on Friday 22nd, nothing extra to pay. Well packed and look like original Toyota parts. Would have been quicker but was delayed a week due to Japanese public holidays from 11th to 15th! booked in to fitted next week so let's see how it goes

Thanks. Amayama say 77 plus shipping so we'll give it a go. Ordered a PCV valve also (part 12204-28020). It's a very easy to use site so that bodes well. Total is under £135 so hopefully only VAT to pay on top rather than customs duty!

Two garages in Poole. Fast-Fit - happy to MOT, Service and do regular type repairs (had brake discs/pads done there). Used these guys for years with various cars, always great service from them. Hamworthy MOT centre - these guys do the after sales work from the local Alphard camper conversion company (Imperial Leisure Vehicles). Sourced and fitted a sliding door motor assembly when mine blew up with the door halfway open (long after I bought it I hasten to add!) - I remembered their name was on the MOT that came with the van and drove over there with it open and said "help!" - they got me going with the door freed and shut and sourced the part within a couple of weeks and fitted it. Legends. Can recommend both garages.

Hi folks, Engine light been coming on over past few weeks (Alphard 2006 2.4 Petrol ANH10), so got a local garage to stick the diagnostic tester on it today. Fault PO171, and the suspect is the EVAP carbon canister because when smoke tested there's fuel vapour literally pouring out of it! Might not cure the fault, but need to get a new one anyway - garage's supplier quoted 500 quid (!) for the part but helpfully supplied the part number (77740-28192). Can find it online from various parts companies in Japan, prices anything from £75 to £150 plus shipping (£20-£40, not sure about customs fees on top of that). Anyone had any experience with ordering from automotomarine_store on ebay (https://www.ebay.co.uk/str/automotomarinestore), or Nengun (https://www.nengun.com/) or Amayama https://www.amayama.com/? Will order and get the garage to replace the PCV valve at the same time I reckon, may as well get it done as these seem to be fairly cheap! Will let you know how it turns out.....

Renewed with Adrian Flux a couple of weeks ago. £100 quid cheaper than last year, came in at £323. 2006 Alphard 2.4 petrol with professional full camper conversion. Fully comp with legal protection, 3 drivers on policy all over 50.

Thank you for this. I'm not going to change it - have ordered 225/55/17 which is what's on there and is the OE spec. Don't want any issues! Have ordered Goodyear EfficientGrip Performance 2 tyres - come with good writeups so let's see how they do...

I'm a muppet. I've just gone to check again as it didn't feel right. The tyres fitted are 225/55/17. I misread the (dirty) sidewall.....so all good. Note to self. Double check next time before spending two hours on tyre websites.....

Insured our 2006 2.4 petrol with full camper conversion done professionally with Comfort Insurance, it's Aviva undewriting it though. Fully comp, 0% no claims (don't ask) for me and the better half, 500 quid. Due for renewal in July so will shop about but we went with Comfort last year because when I tried a few of the bigger companies, no-one wanted to touch it! I'll try Aviva direct at renewal time.

Hi I bought a 2006 ANH10 about 9 months ago, converted to a full campervan spec. Loving it, but it's got the Japanese tyres from when it was imported on it and whilst they look to have plenty of tread they appear to be 10 years old so want to replace them. They are 255/55/17 and I can't find these tyres anywhere, it seems to be an unusual (at least for the UK) size! So I did some digging and this site https://www.wheel-size.com/size/toyota/alphard/2006/ seems to indicate that the stock size for my Alphard is 225/55/17 (or for 16 inch rims, 205/65/16) - considerably smaller! I'm wondering if the previous owner in Japan put some bigger tyres on for looks. If so this might also explain why my fuel economy is even worse than I thought it would be....also if they are the wrong size then my speedo is going to be out (not by a lot according to https://tiresize.com/tyre-size-calculator/) but stilll... Anyone able to offer any other info that might confirm or contradict my research? Thanks

Hi. Just replaced mine on a 2006 ANH10W. Couldn't get a rear wiper as nowhere stocked the Bosch 409 so bought a refill from halfords and cut it down. For the fronts, I got the Bosch SP26S and SP16 Had the same problem as above with Euro Car Parts - rediculous; they wouldn't sell me the part even though I had the number!