OBD2 Trouble Codes 170 & 173 on 1999 Montero 3.5L
(actually a Japanese Pajero imported into New Zealand in 2010)

Does anyone have any suggestions. Each time I clear these codes they come back on, after a couple of hundred miles. Pretty smart mechanics are telling me not to worry about it, but it means that other errors could be masked. So I bought OBD2 Auto Doctor software for Mac ($40) and OBD2 WiFi transmitter ($20) so I can monitor and reset it.

Actually I read on the OBD forum about another Montero owner who had the same problem and fixed everything imaginable including O2 sensors and MAF (Air mass flow meter) and the error still kept recurring.

In my case the mechanics have:
- smoke tested the manifold for leaks
- replaced spark plugs
- replaced oil and filters and added oil additives ProMa
- Wynn's valve lifter additive
- checked O2 sensors
- checked exhaust recirculation circuit EGR operation
- replaced air filter
- checked injector pump fuel pressures multiple times.

They wonder whether it is dirty injectors and suggest an overhaul or maybe a sticking tappet. But it has had an injector service quite recently.

Any ideas from the forum would be welcome. Thanks.

 

PS. The engine runs very well, without the slightest sign of trouble. The error code P0170 is "Fuel Trim Bank One" and P0173 is the same for bank 2. Apparently this means the system thinks the mixture is too lean and in trying to correct the problem by making the mixture richer it has reached the allowable limit of correction.

I think it is very significant that the error is occurring in BOTH banks and is therefore unlikely to be a single oxygen sensor or a single fuel injector playing up. More likely the air flow meter (MAF) perhaps. Apparently this is a common and annoying problem on many European cars, including Mercedes Benz and could be more than a nuisance if it prevents the vehicle from passing its 6 monthly emissions (WOF) inspection in New Zealand.