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Re: "CEL" driving me cracy! Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Mon, 25 Aug 2008 13:53:24
In Reply to: "CEL" driving me cracy!, F. Davalos, Mon, 25 Aug 2008 08:37:59 Members do not see ads below this line. - Help Keep This Site Online - Signup |
As others have noted, any OBDII reader will work. I picked up a cheap Acton one a few months back, if nothing but to clear codes.
The Tech II will provide more information, and could also be used to troubleshoot. But...
The front O2 sensor signal should swing between 0.2 and 0.9 volts (or so), at idle, at a once per second rate. It should spend about 50% of the time above 0.5 volts, 50% of the time below 0.5 volts. You should be able to see the signal swing with a good ANALOG voltmeter; a digital voltmeter has a sample rate, and you'll be able to see voltage changes, but not the 50-50 duty cycle.
The ECU adjusts the mixture to swing the oxygen content around the stochiometric ratio, which gives 0.5 volts on the O2 sensor. The controller swings the mixture slightly rich then slightly lean in order to make the 3-way catalyst work properly. The signal from the O2 signal has limited authority; if it says it is running lean, the controller will richen up the mixture. But only to a point (authority). If the ECU has enriched the mixture to the limit, the O2 sensor crying lean won't make a difference. The sensor will be stuck at the lean (or rich) end of the scale. When that happens, the O2 sensor fault is generated.
When the car is underway, the signal is treated differently; under acceleration and deceleration the ECU schedules fuel other than by the O2 sensor, and the ECU won't fail the ECU when it isn't controlling fuel.
So the sensor may be telling the truth. Stick a voltmeter on the signal level of the sensor and see what it does. Then pull the spark plugs. If the O2 sensor is reading lean (0.2) volts, and the spark plugs look lean, then you've got a vacuum leak or low fuel pressure. If the O2 sensor is reading rich (0.9) volts, and the plugs look rich, assume you've got a bad FPR or leaky injectors.
If the O2 sensor reads lean (0.2) and the plugs look rich, or vice versa, the O2 sensor is bad.
As to the heater circuit - it's just a heater, and the usual failure mode is to fail open. And I believe that a bad heater generates a different code than a bad O2 sensor. All the heater does is get the O2 sensor hot faster for reduced emissions. If the CEL comes on in the first couple of minutes of driving a cold engine, yes, you might have a bad heater. If it comes on immediately, or after the car has been running for a bit, it's not the heater.
So stick a meter on the sensor and check the plugs.
posted by 192.249....
, Tue, 26 Aug 2008 06:20:55
, Wed, 27 Aug 2008 06:53:09, Wed, 27 Aug 2008 05:51:36, Wed, 27 Aug 2008 06:56:44, Wed, 27 Aug 2008 14:30:23, Thu, 28 Aug 2008 05:28:29, Mon, 25 Aug 2008 13:53:24 <-- Viewing This Message, Mon, 25 Aug 2008 14:45:06, Mon, 25 Aug 2008 11:14:16, Mon, 25 Aug 2008 16:25:58, Mon, 25 Aug 2008 17:19:35
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