Howdy,

Any fuse for the O2 sensors? I've located the relay/fuse box next to the battery, not familiar with the large fuses in there. Obvious when they burn? The driver's side dash fuse panel has the fuses I'm familiar with, but the diagram on the cover doesn't seem to describe all the fuses. Can't seem to locate a diagram for either panel. Any other fuse locations?

Thanks,
Geoff

 

Same fuse that runs the coil runs the 02 sensor heaters. If the van starts and runs the fuse is good.

Why are you looking for the fuse? Have you checked for power at the wire harness for the sensor?

 

While watching the PCM data stream for the post cat O2, it takes over 7 minutes of running at idle for it to start to respond. No codess, none pending.

Also wouldn't mind the knowledge...good to know the coil/O2 share fuse.

I ordered a used FSM weeks ago, my first eBay transaction. Got to my local FedEx hub in 3 days, tracking showing it would take 7 days to go the final 30 miles. Turns out it went AWOL at the local hub. Hope it helps the pilferer's Dodge!

Thanks,
Geoff

 

That should be normal since the engine is not up to tempature yet and the computer is still in OPEN LOOP at that stage. Once it is up to operating temperture then the computer will go into CLOSED LOOP and be using all of the sensor information to mangage fuel ratio.

 

I was thinking the O2 sensor heater would get the sensor to switch over sooner. The brand new NTK I installed this AM (thank you hot wrench!) starts to make signal voltage after 3 minutes from cold start, for my van...

This may help someone--after doing some research I've learned Chrysler PCMs use a bias voltage of 1 volt on the O2 sensors, this is contrary to what I'm used to seeing on VW/Audi/BMWs or Fords. This seems to be for the PCMs on 1996 to MY 2000--2000 up run a 5 volt bias voltage. Though I've read on many Dodge forums the Bosch O2 sensors are 'junk' and fail quickly, I think the issue is as much to do with the Dodge's high bias voltage. I've run dozens of Bosch sensors in cars for hundreds of thousands of miles and don't recall any early failures.

Before the O2 heaters get the sensors hot enough to start generating a signal, a live data scanner will show 1 volt (even if the connector to the sensor is disconnected), then when the sensor gets to temp, it will start switch. If the heater circuit is shorted to the signal circuit you'll see over 1 volt.

On the OBDII cars I've worked on prior to my B3500, the downstream O2 sensor(s) just read catalyst efficiency. From what I've read, at least on the 96-2K MY PCMs, the upstream and downstream BOTH contribute to A/F mixture control. Though the downstream to a much lessor extent.

In my post "New PCM in my Future?", I described a random rough idle, power loss and intake backfire condition, without any codes being set. I did notice the downstream O2 sensor was showing 1 to 1.5 volts from time to time during idle, should have set a P0138 but did not. The PCM will turn the heater on anytime the sensor drops below operating temp, and this can happen at idle. I think I was getting voltage bleed from the heater circuit into the sensor circuit, after replacing the downstream sensor, I'm getting live data below 1V and below the front sensor voltage signal, when at temp.

Don't know if this will solve my issue though!

Geoff