Can't get OH monitor to set to ready state
 

I need this monitor so I can pass the NYS inspection. (The evap one has never set ready and NYS says you can only have one not ready monitor) Car is a 2002 SS 6 spd with factory installed SLP Exhaust and intake.

No codes but I reeplaced all the O2 sensors as they had almost 100K on them. Checked the voltage when engine was cold with the key turned to on position but car not started. Ground wire is good. 12+ volts on power. Other wires read @5.3 volts and 4.9 volts.

The OH monitor worked fine setting itself up until about two years ago. Then it wouldn't set. (somebody was able to do it for me but I can't get in touch with them to ask them how) I don't want to tune them out as I suspect at least one cat is going and I want to get it replaced under the GM TSB. Any help or suggestions would be appreciated.

Thanks,
Steve

The car must complete the "Drive Cycle" in order to pass the monitor sequence. Try this & see if it helps. You will need a co-pilot and a scan tool to see the tests being completerd. One person drives the car exactly as described below, and the other watches the scanner to see which tests are being completed. If a test fails, then you must fix the problem. If the same tests are continously bypassed, the PCM may need to be reflashed.


General Motors Driving Cycle

A complete driving cycle should perform diagnostics on all systems. A complete driving cycle can be done in under fifteen minutes.


To perform an OBDII Driving cycle do the following:

1) Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.

2) Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.

3) Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.

4) Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.

5) Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.

6) Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same diagnostics as in step 3.

7) Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.

8) Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.

Z28Pete,

Thanks for the reply. However, as you can see from your drive cycle doc it appears the O2 heater should set fairly quickly (step 2). It's not doing that (and it had in the past)

I also see in step1 it says "Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.

I always take the key out so that's not a problem. However, could the ignition mechanism think that the key is for some reason in there and that's why it's not running? How would I check for that?

You could use a Voltmeter and go across the heter leads on the O2 sensor, and there should be no voltage with the ignition off. Easier if you unplug the O2 connector and look back towards the PCM.

pete, are these diagnostics from the drive cycle built into the cars computer? if i do it, would it throw a check light?

The diagnostics are built in, and the computer runs them whenever a certain set of condition are met. The conditions are as shown on the chart. The CEL may be lit if certain tests failed. The computer stores all the info and when queried with a scan tool, it will show which tests were run and wether they passed or failed. It usually takes a few days of normal driving for the PCM to get around doing all the tests automatically.

ohh okay, thanx