22 replies to this topic

[Bakazan]

What is the expected voltage for the post cat O2 sensor?

 

I'm getting P0140 and P0141 error codes. Reading the sensor output on Torque Ap it is giving a steady reading of 0.2V raising when the engine is revved then dropping back to 0.2.

 

Does the EML throw a different code if it suspects a problem with the CAT itself?

 

At steady state the first one wangs up and down between 0 and 0.7/0.8V as expected.

[slindborg]

Should switch 0.2 to 0.8 ish at a similar rate to the precat

[Bakazan]

Ok, so the sensor is buggered, I just wanted to rule out that it might be something simple like an intermittent fault in the wiring.

 

Thanks for.your help.

[Mangham54]

Continuity test the sensor.

[Bakazan]

Continuity test the sensor.

 

Across the the heater circuit? Which colour wires?

 

Thanks

[slindborg]

white and white

[Johnboyhgt]

Pre cat sensor switches between 0.10 and 0.80 mv 

 

But post cat is used to check catalyst efficiency. with throttle steady 2000 rpm and engine fully warm the voltage should be in the range of 60-85mv steady reading with very few fluctuations.

 

easiest way is to use a diagnostic machine with both readings showing at once. if both match then i'm afraid its the catalyst thats burned out. usually caused by a misfire of some description ie coil packed up and driven for a length of time.

 

PM me if you need more help.

[slindborg]

well the lambda cheaters shouldnt work in that case .... oh hang on they do

 

0.2 -> 0.8 ->0.2 changing every 3seconds.

[Johnboyhgt]

well the lambda cheaters shouldnt work in that case .... oh hang on they do

 

0.2 -> 0.8 ->0.2 changing every 3seconds.

 

Providing it doesn't switch at the same rate as pre-cat the ecu wont trigger cat efficiency errors.  and as they switch at 1 hertz and not 3 in your case all is good !!

[Johnboyhgt]

Only exception would be wide band sensor and they arent used post cat.

 

Also 0.20mv is very lean on that engine would expect at least 0.60mv

 

 

Do you have an air leak somewhere ? or perhaps low fuel pressure etc ??

[slindborg]

no WAY!!!!!!!

 

 

 

 

 

 

 

 

 

 

 

[slindborg]

Oh and for reference, its 0.2V not mV

[Johnboyhgt]

0.200v     as the last digit isn't shown by most instruments     Millivolts !!!!!

 

 

• mV, millivolt: 1/1,000 of a volt, a measure of electrical potential  

 

 

 

 

[slindborg]

so youre actually doing this....

 

You said 0.1 to 0.8 mV..... and its actually 0.1 to 0.8V..... mild difference. But no, lets cock it up a treat for the OP to try and diagnose something

[Johnboyhgt]

well the lambda cheaters shouldnt work in that case .... oh hang on they do

 

0.2 -> 0.8 ->0.2 changing every 3seconds.

 

You started it, I dont do ridicule !

[Johnboyhgt]

What are your error code descriptions ?? 

[slindborg]

 

well the lambda cheaters shouldnt work in that case .... oh hang on they do

 

0.2 -> 0.8 ->0.2 changing every 3seconds.

 

You started it, I dont do ridicule !

 

 

I never quoted scaling, granted, but.... ah fcuk it.

[Johnboyhgt]

Any way your error codes give it away, see below

 

 

[color=rgb(0,0,0);font-family:verdana, sans-serif;background-color:rgb(221,221,221);]P0140 - 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)[/color]
[color=rgb(0,0,0);font-family:verdana, sans-serif;background-color:rgb(221,221,221);]P0141 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)[/color]

 

Without taking a look i cant be sure but logic would say that either your wiring is causing trouble or your lambda is knackered, best way would be to use a multimeter and check the resistance between the two white wires on the post cat lambda plug.  Cant remember the exact resistance but perhaps sindborg could add that bit ??
 

[slindborg]

nope, I dont want to be right wrong again.

[Johnboyhgt]

nope, I dont want to be right wrong again.

 

Just make sure theres some resistance (12 Ohms seems to ring a bell but not 100%).

 

If you cant do the resistance check and the wiring looks fairly good ie no corrosion in the plug its a fair bet the sensor is knackerd.