Check Engine Soon light? 2003 F-150

[SpiderGearsMan]

Re: Check Engine Soon light? 2003 F-150

bank one sensor2 - post cat
you will have very littler acrtivity on that - if it reads the same as sensor one - means the cat is not working
p0420 or p0430

[JeffMcKC]

Re: Check Engine Soon light? 2003 F-150

Bill pretty much as on any, the primary O2 in front of the sensor .50 volts is Stociometric it cant stay there so it will go rich above .5 then below .5 lean the ones be hind the cat after being cleaned up should be steady and read close to the .5 they will work once warmed up by the exhaust without the heater but at a idle cool and quit, you have a heater code and should have a heater "PID" to look at.

[CDMBill]

Re: Check Engine Soon light? 2003 F-150

So on the way to the parts store I set up the Actron to read the live data, PID's, and to make my day the check engine light had gone off by itself, I did not clear the codes. When I ran a code check it gave the same code as before P0141.

The good news (?) is that when parked at idle rpm or driving on the highway the real time indicators for the two pre cat and the two after cat sensors tracked pretty consistently with each other. I saw a lot more variance with throttle inputs on the two pre-cat sensors than the two post cat sensors which seemed to be both more stable and have more latency, that is they change more slowly and with much lower voltage swings. The average seemed to be in the .520 - .570 range.

I bought the sensor anyway but I ran out of time to check the harneses and given the PID's looked good (to me anyway) and the light went off by itself I am not in a panic.

[min301]

Re: Check Engine Soon light? 2003 F-150

Replace the sensor, clear the code, and you'll be golden.

[Darren N.]

Re: Check Engine Soon light? 2003 F-150

I'm following along attentively. I don't have an OBII scanner yet but I'm trying to resolve similar issues on my '02 Crown Vic. I just ordered a new set of O2 sensors from RockAuto (at 100k+ miles they should probably be changed anyways). My Check Engine light came on so I cleaned the MAF, TB and intake elbow and the light went off. However, my fuel economy has gone south and now the engine is idling much higher than normal.

The data logging feature on your scanner is pretty neat, this kind of troubleshooting is new to me. I think I'm really going to have buy one of these scanners!

I'm truly impressed by the amount of knowledge here, awesome stuff guys! I'll sit back down now and continue taking notes :P

Keep up the good work.

[CDMBill]

Re: Check Engine Soon light? 2003 F-150

Darren, like you I'm learning this stuff for the first time from the experts here. The one O2 sensor cost me $50 and the Actron was $100 online so I'm thinking if you retruned one sensor and bought the tool you are halfway there. My buddy from whom I borrowed the Actron has a 62 Ford F100 sitting on a complete '04 Merc Marauder chassis/engine/trans setup which is why he bought it in the first place. I'm the test monkey with my truck.

[milner351]

Re: Check Engine Soon light? 2003 F-150

Bill
The only reason the post cat O2 sensors are there is because of an EPA catalyst monitor mandate.

When the pre and post look the same - your catalyst is worn out and the EPA requires the check engine light to come on to warn you of this condition.

The primaries (pre cat) do all the feedback control of the mixture, the post cats are really only a watch dog for the cat.

[JeffMcKC]

Re: Check Engine Soon light? 2003 F-150

AND the heaters just make them read quicker and stay active on long idles when they might cool down

[CDMBill]

Re: Check Engine Soon light? 2003 F-150

Very interesting and it explains the much wider swings I saw on the pre-cat sensors. So the loss of a post cat sensor will throw a code and cause a vehilce to fail and OBD scan for renewing tags but doesn't affect the tune of the vehicle itself, right?

I finally get around to making the change this weekend, test the leads for the harness ,and will rset the code and hope for the best.

Thanks to everybody for all the great advice and help.

[CTX-SLPR]

Re: Check Engine Soon light? 2003 F-150

Some vehicles seem to have some sensitivity to the rear O2's being out of whack but mostly having a miss matched pair sometimes can cause the computer to think the cat is busted because the fronts are reading great and the rears are old and not responding well. I think there is a marginal effect on the way the vehicle runs without the rear sensors but who know if Ford decided to "motivate" you to keep them replaced by causing some sort of "abuse" mode due to them being out of whack.

[SpiderGearsMan]

Re: Check Engine Soon light? 2003 F-150

we are currentlr pulling our hair out with a kia three way cat system
the third cat does not have a post cat o2 -ver odd - setting p0430s

[JeffMcKC]

Re: Check Engine Soon light? 2003 F-150

Its all about the tail pipe

[CDMBill]

Re: Check Engine Soon light? 2003 F-150

Just to close the loop, I swapped the sensor, $49 from O'Rielly Auto Parts, checked the supply voltage which was fine and erased the code.

All goodness, thanks for the help guys.

[Darren N.]

Re: Check Engine Soon light? 2003 F-150

That's excellent news, Bill.

I've been playing around with a similar issue on my Crown Vic. I disconnected both rear O2 sensors to see what would happen and to my complete surprise, the ECU did not give a damn! lol No Check Engine light and the engine ran fine. I received my O2 sensors from RockAuto last week, both fronts and rears. Like CTX-SLPR mentioned, I wonder if rear O2 sensor failure has any real effect on engine control... what a freakin' scam. lol :D

Cheers and here's to many trouble-free miles ahead!

[TC]

Re: Check Engine Soon light? 2003 F-150

Some vehicles seem to have some sensitivity to the rear O2's being out of whack but mostly having a miss matched pair sometimes can cause the computer to think the cat is busted because the fronts are reading great and the rears are old and not responding well. I think there is a marginal effect on the way the vehicle runs without the rear sensors but who know if Ford decided to "motivate" you to keep them replaced by causing some sort of "abuse" mode due to them being out of whack.

Rear O2 sensor do nothing other than tell the computer to dump more fuel in to cool down the Cat so that it doesn't overheat(burn up).

I have personally disabled(in the programming) the rear O2 sensors on my '99 Z28 due to the fact that I don't have cats.

It is the O2 sensors before the cat that do all the monitoring of the A/F ratios, the ones after the cat have no effect on the A/F's.

Basically if you car throws a code for a rear O2 sensor it will be a bad O2 sensor, a problem with the wiring, or the Cat is bad.

Now saying this I've had codes thrown before and just cleared the codes and they never came back. So sometimes glitches happen, I would clear the codes and see if it resets them, then you know you really have a problem.