Code 25, running Lean.

[Angry7M]

Ok so im getting a code Running Lean 25, its been on for a long time now. Ive checked many things and fuel pressure is good, no problems with that. Today I checked my O2 sensor Heater resistance.

When Cold it read around 6.8 Ohms

At normal operating temp it read around 12 ohms.

THe Hayness manuals says it need to read from 3.0 to 3.6 ohms.

So I guess this means I need to replace the O2 sensor?

This is an Denso Sensor I bought at Autozona, its a universal type thats suppose to work with the 7MGTE.

I always get this check engine light cruising at around 55mph, and it stays on.

Maybe the O2 sensor that I bought at Autozone is not the correct one? Does anyone have the Densor Part Number for the replacement I need? Thanks

 

[Angry7M]

anyone?

 

[jetjock]

You're barking up the wrong tree. First, heater resistance is dependent on temperature. Second, the heater is mostly irrelevant to O2 sensor operation once the engine is hot. What you should be checking is sensor voltage and not the heater. And while it's possible a bad sensor can cause 25 a great many other things can also. Drive the sensor full scale both ways to see if it responds. If it does there's nothing wrong with it and the leaness is real versus a lie caused by a bad sensor. That would point you towards any of the other things that could cause an actual lean condition. Or you could just throw parts at the car. That would seems at odds for someone apparently too cheap to buy a TSRM though...

 

[Angry7M]

Ok thanks for clearing that up. I was wondering what you mean by run the sensor full scale both ways? How would I do that?

Also reason why I didnt check the O2 using the TSRM is beacause I only have a Digital Multi Meter, and I would appearently need a regular volt meter to perform the test. Thanks

 

[Angry7M]

BTW I just got a Code 71 EGR Malfunction. I think ive read somewhere that the EGR can cause a Lean conditon. Is this true?

I get this code once In a while, but not always.

 

[jetjock]

1) Actually a "regular" voltmeter (I assume you're referring to the D'Arsonval movement/galvanometer type) would be bad because the input impedance is typically too low.

2) While measuring the sensor at 2000 rpm snap the throttle wide open then closed. Sensor should go full rich (800 mv or higher) then full lean (200 mv or lower). You could also pull the brake booster line to drive it lean. Shoot some carb cleaner or propane in there to force it rich. If it responds it's working and reporting the truth. Look elsewhere for what's causing the lean condition.

3) Code 71: Means the temp in the EGR passage didn't rise to the level expected by the ECU. Measured by a thermistor sensor that looks for exhaust gas heating when the EGR valve is opened. Problem could be a bad sensor, wiring, clogged EGR passage or something that prevents the valve from actually opening. VSV, bad modulator, leaking EGR vac hoses, etc...

 

[Angry7M]

I did the test JJ told me to. The Mutli Meter would read 165 at idle, when I started to rev it up it would read in the 300's and when I did the throttle snap test it bearely went up.