I have a 2002 QC with the 5.9l, so I thought this question be best suited here with the 2nd gen guys. My truck through a P0138 error which is the downsteam O2 sensor shorted to voltage. I am in Canada so I only have 1 converter so I have have 1 per and one post sensor. I reset the codes and it came back. The first of the summer I completly replaced the exhaust from y- pipe back due to rust. I did not replaced the sensors. I don't believe the cat is the issue as I only have 1000 km on since the new exhaust, but I might have a slight manifold leak as the exhaust does not sound the same. My question is, has any one had this error and found the issue was a leaky manifold. I know the hemi's are prone to broken manifold bolts, but are the 5.9's also?

 

I would trace the wiring to see if it is damaged or the insulation melted. Look for places it could rub against anything. If it shows a short, something that should have a + value is at 0 to equal ground. It could be in sensor itself.

 

Have a read https://dodgeforum.com/forum/2nd-gen...ng-the-o2.html

 

unless you find damaged wiring in the exposed area close to the O2 sensor, i'd assume the heater circuit in the sensor is shot.

you might can test that with an ohmeter. compare the results to the front sensor. i'd expect some resistance between the white heater wires and the ground. i'm not sure what i'd expect on the signal wire??

 

Checked the wiring and found no exposed wire or melted insulation. On the sensor there is 2 white and 2 black wires. To meter the sensor what am i comparing the resistance from each white wire to ground? How do I know which of the black wires is ground, and which one is the signal wire?
With the non-fouler trick, does this effect fuel ecconomy? Is there any dangers in doing this to the truck?

 

here's some general info from dodgeram.org, but the colors are for older years.

what i'd do is ohm out each wire to a frame ground. the 2 whites (heater) and the signal should have some resistance. the ground should have zero resistance.

according to NGK, black is signal and gray is ground.

http://www.ngksparkplugs.com/images/...t_11-16-04.pdf


http://dodgeram.org/tech/gas/Trouble/O2_sensor.htm

 

Check ohms between black wires, then ohms between white wires. Should be VERY close (within 0.0 to 0.2 ohms max) difference with other O2 sensor. You can check each wire to the O2 body, but I think it should read 0 ohms. I would have to check an extra O2 sensor when i get back home tobe 100% sure.

 

Ok I ohmed out the post sensor and found that measureing between the 2 white, between the black and grey, and than each wire to chassie ground, had identical readings as the pre sensor. On the link that dhvaughan gave for troubleshooting O2 sensors. It states that if you measure the voltage between the sensor ground (grey wire) to the Black (signal wire) on cold start up should read 0.1-0.2 volts. then in cold loop mode read 0.1 to 0.9 volts. Here is what mine did.

On start up 3.4 volts
after 5 mins 1.8 volts
after 10 mins 1.3 volts
closed loop back to around 3.4 volts

In the link it states that if the post sensor is measuring above normal, the pcm will adjust the goal voltage lower, causing the a lean fuel mix which can cause a spark knock. I believe this is why I thought I might have a broken manifold bolt causing a leak, due to the truck sounded different. I think I will suck it up and get a sensor at the dealer,,,unless someone out there believes that the higher voltages cold be related to something else....any input.

 

Anyone have any input?

 

Yea, replace it.