Manager Forum

This car is taking frustration to a new level. This car, an 03 Pontiac Grand Am GT with a 3.4L engine an 102,000 miles on came in for emissions inspection an it had a code PO401. We diagnosed a faulty EGR valve, replaced it an proceeded to reset the monitors for emissions inspection. The one that has not reset is the one for the heated O2 sensor. Mode 6 shows no faulty data, I can manually do the heater test with my scan tool an it works, why wont the readiness monitor set to ready? What am I missing or is there something I need to do? Typically this is a piece of cake thing but not so with this one.

As a rule I'll drive the vehicles to reset. The heater circuit may need a few other monitors to be reading before it runs. Sometimes the fuel level has something to do with the emissions running.

Well Steve, I agree with ya. The fuel level is just barely below the 1/4 mark. Here in PA for an 03 model all but one monitor needs to be reset be4 emissions inspection can pass. I typically do not get excited if an evaporative systems monitor does not reset cause that one is usually the most difficult to run. The drive cycle for the O2 heater test is to start the engine with coolant temp below 122 degrees, idle in drive for 2.5 minutes with foot on brake, ac and rear defroster on, then drive at 55-60 mph for 3 minutes. Well I have done this time and time again with the same result - the heater readiness monitor does not switch to "Ready". It is so frustrating cause we dont have time for this an the customer wants his car. We get stuck in between the state an the customer in a case like this.

There are two stages to the monitor according to my information. The second part requires an engine temperature of 176 degrees minimum to finish. Perhaps the engine is running just slightly cool enough to not get past this but warm enough to not set a PO128?

Totally forgot that. A bad t stat will cause that as well as a bat cts. I hook up my scanner read the operating temp and hit the rad and where the upper rad hose attaches to the engine with an anfared temp gun. If this had a heavy duty radiator you may need to disable the fan or restrict the air flow. Great point on the temp, I totally pulled a blank on that one.