Check engine light error code 172

On long highway trips (CA to CO and back) in my '95 Explorer V6, the check engine light comes on at various times during the trip, but never after reaching either destination. Within Colorado I've driven up to four hours with elevation changes of 6000 feet, but the light never comes on in those cases. Auto Zone says the error code is 172, which they said refers to an O2 sensor indicating lean mixture in one bank (don't remember which). Is this likely to be the sensor itself or something else? How hard is it to replace the O2 sensor?

Reply to
Richard
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The code refers to the right bank of the motor (bank 1) and roughly indicates that the PCM hasn't seen enough activity from the sensor..... it is staying on the lean side of stoichiometric. While the sensor may indeed be faulty, my experience shows the sensors to be very dependable and (unless there is another condition present) seldom in need of replacement.

Since your problem seems to happen at speed, I would concentrate on the conditions we see at speed. We can rule out intake manifold leaks since these would normally give us problems at low speeds - however, it wouldn't hurt to be sure the air filter and MAF are both clean. Exhaust leaks upstream of the sensor should be repaired and the condition of the ignition system should be checked..... your Ex has a waste spark (EDIS) ignition system.... the plugs on the right hand side fire from the ground electrode to the centre electrode - be sure that you don't have single platinum plugs installed as these could misfire at highway speeds leading to high oxygen content in the exhaust stream. If you want to run platinum plugs, be sure they are of the "double platinum" variety.... i.e. both centre and ground electrodes are platinum. Electrons will "jump" from a sharp corner much more readily than from a flat or rounded surface.

I would probably change the fuel filter and monitor the fuel pressure at highway speeds to ensure that I'm not inducing a slightly lean condition that could help create ignition misfires.

Simply replacing the O2 sensor might mask any underlying problems for the time being but without the additional diagnostics, we have no way of being sure...

HTH.

Jim Warman snipped-for-privacy@telusplanet.net

Reply to
Jim Warman

Fault code 172 is defined in SAE J2012 as "System to Rich - Bank 1". I'm not sure if the 95 Explorer followed SAE fault code definitions, but certainly later models do. Fault Code 171 is the lean malfunction.

Under any case, even if the engine is running rich, most of the checks Jim mentioned would still apply. MAF sensors are known to be problematic in these years, that is, they tend to give biased readings as they age. However, the typical failure of the MAF sensor is to produce biased-high signals in the lower range, and biased-low signals in the higher range. Which tranlates to a rich engine at idle and low speeds, and a lean engine at higher speeds.

Hope this helps,

Tom

Reply to
Tom

Richards Ex is an ODB1 car and the code Tom is thinking of would be an OBD2 code - P0172 (which is indeed a rich code).... however, the Ford 2 and 3 digit codes are proprietary and bear no resemblance to the SAE standards. OBD2 standards were mandated to simplify things for the aftermarket (indepedant) repair shops. P0172, therefore, means exactly the same no matter what make or model.... the conditions that generate it may vary slightly but the code is still translated the same.

When we discuss trouble codes, it is ever so important to refer to them in their complete context.... OBD2 codes are represented by a letter (denoting which system generated the DTC) followed by four numerals. "P" codes are powertrain, "B" codes are body, "C" codes chassis and "U" codes are network communications codes.

HTH

Jim Warman snipped-for-privacy@telusplanet.net

Reply to
Jim Warman

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