firefighter_0029 Posted April 4, 2007 Report Posted April 4, 2007 Can anyone tell me what a P0420 code is on my 02 Bonneville? I would imagine it would be the same as the code on 02 GP w/ a 3800 Series II. Quote
runt Posted April 4, 2007 Report Posted April 4, 2007 P0420 - Catalyst Efficiency Below Threshold (Bank 1) More than likely O2 sensor. If I were you, I'd do both just to make sure that the back one wasn't messing up the front one. Quote
terryk2003 Posted April 4, 2007 Report Posted April 4, 2007 that code should be the back one...it measures catalyst effeciency AFTER the converter...otherwise, how the hell would it measure how efficeint it was!? ...i'd say its either a bad 02 sensor or a bad cat... Quote
digitaloutsider Posted April 4, 2007 Report Posted April 4, 2007 The rear O2 sensor probably shit out. Or the cat's bad. Quote
RJansen658 Posted April 5, 2007 Report Posted April 5, 2007 that code should be the back one...it measures catalyst effeciency AFTER the converter...otherwise, how the hell would it measure how efficeint it was!? ...i'd say its either a bad 02 sensor or a bad cat... Nope... the way that it measures efficiency is by comparing the post cat O2 reading to the pre cat O2 reading, the difference in signal tells the ECM how much emmisions were reduced. EITHER sensor (or both) can cause this, as can a bad cat, or improper air/fuel ratio. Quote
firefighter_0029 Posted April 5, 2007 Author Report Posted April 5, 2007 If the O2 Sensor was bad wouldn't it come up saying "O2 Sensor"?? The reason I ask is because the O2 sensor is bad in my S-10 and the code comes up Secondary O2. Quote
RJansen658 Posted April 5, 2007 Report Posted April 5, 2007 No. Not neccesarily, the sensors reading varies farther and farther from true over its lifespan. The technical term is sensor skew. Innacurate reading, in order to get a code there usually has to be an electrical failure, or the ECM reads a value it knows isn't within the sensors ability to measure. Quote
terryk2003 Posted April 5, 2007 Report Posted April 5, 2007 the more i look @ that...its most likely a bad cat... Quote
runt Posted April 5, 2007 Report Posted April 5, 2007 I've been getting the same code. Only happened after I got my ZZP 2.5" D.P. with "high flow" cat. So I hoping 2 new sensors will fix that. Quote
firefighter_0029 Posted April 5, 2007 Author Report Posted April 5, 2007 Does a O2 sim effect the gas mileage alot? Quote
terryk2003 Posted April 5, 2007 Report Posted April 5, 2007 Does a O2 sim effect the gas mileage alot? 02 sim on the rear shouldnt affect milage much, if @ all...the rear 02 is basically there to check the catylatic converter... Quote
runt Posted April 5, 2007 Report Posted April 5, 2007 Does a O2 sim effect the gas mileage alot? 02 sim on the rear shouldnt affect milage much, if @ all...the rear 02 is basically there to check the catylatic converter... Agreed. Quote
digitaloutsider Posted April 5, 2007 Report Posted April 5, 2007 The rear O2 has absolutely nothing to do with ANYTHING side from making sure the cat works. Quote
RJansen658 Posted April 6, 2007 Report Posted April 6, 2007 Thats correct, the upstream O2 is used to control fuel pulse width, IAC stepping, and EGR flow whenever the ECM is in closed loop operation. The only purpose of the downstream O2 is to measure catalyst efficiency. Quote
RJansen658 Posted April 6, 2007 Report Posted April 6, 2007 Thats correct, the upstream O2 is used to control fuel pulse width, IAC stepping, and EGR flow whenever the ECM is in closed loop operation. The only purpose of the downstream O2 is to measure catalyst efficiency. And to add to it.... Bear in mind that it although the downstream sensors only purpose is to measure efficiency, it still does this by comparing it to the upstream O2's reading. Granted a faulty upstream will usually produce other codes as well, because it effects the EGR system, etc. The easiet way to determine the culprit is with a scan tool capable of sensor readings. Generally, the O2's will stay within a certain range when the car is running at temp, there is a visible low point and highpoint, this is caused by the ECM adjusting fuel pulse width for emissions purposes. You can generally watch both sensors output in millivolts with the scan tool, and watch the fluctuation on the upstream, the downstream should be just a bit behind it, meaning as far as going thru its range from low to high. It will be changing too fast to watch, so use the scan tools graphing function. Its hard to explain how to determine the bad sensor, but if you had some graphs of the sensors I could point it out. A correctly operating sensor will move thru its warmed range quickly, producing readings that almost follow neat steps when graphed. You should never get a richer reading downstream than you do upstream. It isn't possible, and indicates a defective sensor. the scan tool will show the output of the sensor in millivolts, which is just a breakdown of volts. The sensor range for ALL O2's is 0-1.1 volts. Combustion engines need the proper air fuel ratio to operate correctly. For gasoline its 14.7 parts of air to one part of fuel. Too much fuel, and all available oxygen is consumed and exhaust gasses contain almost no oxygen. This produces a upstream reading greater than 0.45 volts. Not enough fuel, it all gets burned, and excess oxygen enters the exhaust, causing sensor voltages lower than 0.45 volts. Usually the output range seen is 0.2-0.7 volts. But a perfecty tuned reading is 0.45 volts, meaning at that reading, you are not too rich or lean, just right for maximum combustion power. Quote
firefighter_0029 Posted April 10, 2007 Author Report Posted April 10, 2007 I changed both sensors and the light went off thanx guys!! It starts alot better now too. You wanna help me with another one?? I have a 96 S-10 2.2 5 Speed. I'm getting a P1406 Manufacurer Control Aux Emission Control It runs fine when Cold but as soon as it warms up about 10mi down the road it starts to jerk, and then it just gets worse. When it first started doing it you could hardly drive it and it gave me the P1406 Code and ones for the TPS and MAP Sensors. I changed both sensors and at least you can drive it but now it started doing it again real bad and now it's just giving me the P1406 Code. And a Haynes Manual tells you nothing about it and I can't seem to get my hands on a Serice Manual for it. I love this truck and now that it's starting to get nice out I really want to drive it. Quote
firefighter_0029 Posted April 11, 2007 Author Report Posted April 11, 2007 Ok now today it is really running like shit!! Now I'm getting a P0106 MAP/BARO CKT Range/Perf ?? and I'm still getting the P1406 HELP!!! Quote
turby Posted April 11, 2007 Report Posted April 11, 2007 How about try the S-10 forum or even the correct section on this forum? Quote
firefighter_0029 Posted April 11, 2007 Author Report Posted April 11, 2007 How about try the S-10 forum or even the correct section on this forum? The S-10 forum Sux!! and RJansen was already helping me with something else. Thanx for your help though. Quote
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