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Re: Is Check Engine Light on
Posted by Bill Homer [Email] (more from Bill Homer) on Sat, 2 Mar 2019 11:48:29
In Reply to: Re: Is Check Engine Light on, Lester, Thu, 28 Feb 2019 09:42:58
1. In my personal experience, the oxygen sensors should put out voltage in the neighborhood of 0.2 VDC to 0.8 VDC. Here's something that I found online: "An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich and there is little unburned oxygen in the exhaust. When the mixture is lean, the sensor's output voltage will drop down to about 0.1 volts." If you have an ANALOG voltmeter (much easier to observe this than on a digital voltmeter), this is easy to measure and watching the needle swing up and down about every two seconds will give you some confidence that the sensor is working. Be sure to measure the output of the oxygen sensor UPSTREAM of the catalytic converter, as the second sensor is used primarily by the OBD-II system to show that the cat is working - pre 1996 cars didn't have this. Using a similar procedure and a special test light is how I set the base mixture on my 1989 Volvo 740 Turbo.
2. Are you sure that the coolant temp sensor is not broken? If it is completely open, i.e. infinite resistance, the ECU will think that the car is in winter in Siberia based on the high resistance and will enrich the mixture accordingly. I'm not sure what the proper resistance range over temperature, but it should be searchable here. I have had to replace this sensor on both my previous 9000 and my 740T.
3. How about the air temperature sensor? Same idea as #2 above.
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