Another CEL tale of woe!

After having the after cat sensor replaced a couple of months ago (which was not long after a warranty replacement Toyta short engine was fitted) the CEL light has now made another appearence, I took the advice and bought a code reader(anyone in the Teesside area who needs a code reading can PM me)  this time it was a code P0175 -too rich bank 2, I cleared the code and cleaned the MAF but a couple of days ago the light came on again this time with codes P0172 and P0175 -too rich banks 1 & 2  and two pending codes which were also P0172 and P0175  

Am I correct in thinking that the MAF requires replcement?

is a possability, but i'd just reset the ECU first

Tried that by removing the ECU and EFi fuses for 10 mins, light went out but came on again after a couple of days   s:shock: :shock: s:shock:

not anywhere near Surrey are you?

Sadly no, I am up in the North East , when the fault codes are cleared they seem to take a couple of days to come back each time.

Quote from: "chazzyw"Am I correct in thinking that the MAF requires replcement?

It could be the MAF, but .. here's what the BGB lists:

• Injector leak, blockage
• Mass air flow meter
• Engine coolant temp. sensor
• Ignition system
• Fuel pressure
• Gas leakage on exhaust system
• Open or short in heated oxygen sensor (bank 1, 2 sensor 1)
  circuit
• Heated oxygen sensor (bank 1, 2 sensor 1)

What it's actually telling you is that according to the O2 sensors, the built in map is causing the engine to run rich.  When it does so, the ECU starts to remove fuel and eventually stops removing it when the O2 sensors go back to reading 'stoic' (14.7:1 air/fuel ratio) under closed-loop conditions.

The fuel trims are then stored and are applied continually - in closed and open loop.

The ECU doesn't light a CEL until the adjustment is more than +/-38%.


So what your ECU is telling you is that it has removed 38% of the fuel from your fuel maps - if this is a sensor fault, then you are now running very very lean, dangerously lean in fact - fortunately you have a knock sensor that will also retard timing if it's so lean the engine begins to knock (which it almost certainly would be) so you'll just be losing power and heating things up a lot more than you otherwise would.


This particular CEL uses 2-trip detection logic, so if you clear it you'll need to drive at least twice before it will come back on.

Personally I would be tempted to do what Stu says, but not simply reset it and then forget about it - reset it and start checking components.

First: Make sure the O2 sensors are operating correctly (if you only have a code reader rather than an OBD-II scantool, you'll need to use a multimeter) - their output should flipflop between <0.4V and >0.55V.

Secondly: Check for exhaust leaks upstream of the O2 sensors (between the head and O2 sensors) - though I would expect that to light a "Too LEAN" code, rather than too rich.

Thirdly: See if you can borrow a MAF - they're not cheap, unfortunately.

fraid you've already tried what i'd suggest, unless anyone else has a suggestion i'd be going with your first suggestion, perhaps someone would be kind enough to lend you one to try first though as they cost £90

Well no sign of knocking and temperature and performance seem ok , would a dodgy 02 sensor show its own fault code? , no sign or sound of exhaust leaks at the maifold /head joint ( I did ask Mr T after the first instance of the CEL light and they tried to sell me a MAF £160 fitted  s:shock: :shock: s:shock:  ) but I can get one from Chris at cheap toyota parts for £90 all in, I guess I  just  needed a second opinion from the experts before I spend the money   s:D s:D

A dodgy O2 sensor might throw it's own fault code (there are several - from "totally dead" to the obscure "Insufficient coolant temp for closed-loop operation" that's actually an O2 sensor fault), but it's not guaranteed..

Start with whichever you can do cheapest, I reckon..  If you already have a multimeter, that'd be the O2 sensors I think.

Thanks Aaron, (and Stu) I will give it a go over the weekend and report back   s:) s:)

How far away from Manchester are you? I have an OBD reader that can monitor a few bits and bats including the O2 sensors and MAF.

Quite a distance I`m afraid, the nearest biggish town to me is Middlesbrough, but thanks anyway.

doubt it will be the 02 sensor though as a dodgy one would lead to a single code for a bank and not one for each bank iyswim