Jeep Garage  - Jeep Forum banner
1 - 16 of 16 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter · #1 ·
My daughter purchased a 2005 Jeep Liberty and loves it. About a month ago she recevied an O2 sensor (P0038) code. I replaced the sensor and all was good until a few days ago. The same error code is back. I replaced the O2 sensor again but this time it will not clear. I checked the connector at the O2 sensor and I am not getting 12 volts to the heater circuit. Is there a fuse or relay that feeds the O2 sensor? If so which one is it?
 

·
The beast from Brazil
Joined
·
8,310 Posts
Welcome to the garage.
For sure there is a fuse for the O2 heaters. Not familiar with the liberty, but some jeeps even have a relay in the heater circuit. Have a look in the power distribution center (relay/fuse box under the hood), you will see on the inside of the cover which relay and which fuse is for what. Did you use original sensor ( also not sure for the liberty, but on the WJ its Denso), because other brands may give problems with slow heating and the PCM sees this as a heater fault.
 

·
The beast from Brazil
Joined
·
8,310 Posts
Also depending on emission package, the O2 heaters are fed via the auto shutdown relay. This relay falls off after some seconds when the PCM sees that the engine is not running. In that case you will not have the 12V at the connector. But did you use original sensor?
 

·
The beast from Brazil
Joined
·
8,310 Posts
The Bosch sensors are very good, but they heat up more slowly then the Denso sensors. If the heating takes too long, the PCM will see it as a fault and set a fault code and switch the check engine light on. I have heard of more guys who used Bosch without problems, but also many others who encountered problems with the Bosch sensors. This is normally solved by using the original Denso sensors.
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #8 ·
Thanks for the input. I still don't have 12 volts at the connector to the O2 sensor. The dealer told me that the PCM module feeds the 12 volts to the sensor, it is not fused or run through a relay.
 

·
The beast from Brazil
Joined
·
8,310 Posts
I don't have schematic manual for the liberty, so can't confirm this. But it would be strange that the PCM would.continue feeding the heaters when the engine doesn't run. On my jeep its also the PCM who switches the heaters, but via the auto shutdown relay. Maybe a member with Liberty wiring schematic could confirm the way its wired.
 

·
Registered
Joined
·
5 Posts
I'm looking at a wiring diagram for the '02 Liberty and there is a oxygen sensor downstream relay in the PDC in the '02 model, but both rear O2's are being feed off of the same circuit; so if you have power at the 2/2 but not at the 1/2 then look for a wiring issue.
 

·
Registered
Joined
·
19 Posts
Also depending on emission package, the O2 heaters are fed via the auto shutdown relay. This relay falls off after some seconds when the PCM sees that the engine is not running. In that case you will not have the 12V at the connector. But did you use original sensor?
hello all. I know this is an old post but I have been trying to research why I dont have 12v at the O2 connector. (code;P0135, P0155) Or at the fuse for that matter. Ive been looking for a reason, PCM, relay, etc. Is the only way to test, is to have someone else turn on key while I already have tester conected ? O2 heater failed ohm test,(B1,S1) I plan on replacing both.
 

·
The beast from Brazil
Joined
·
8,310 Posts
hello all. I know this is an old post but I have been trying to research why I dont have 12v at the O2 connector. (code;P0135, P0155) Or at the fuse for that matter. Ive been looking for a reason, PCM, relay, etc. Is the only way to test, is to have someone else turn on key while I already have tester conected ? O2 heater failed ohm test,(B1,S1) I plan on replacing both.
Yes, the heater will only be powered when the ASD relay is powered. When the engine is not started, then the ASD relay falls off after some seconds. You could try and measure at the fuse with the engine running.
 

·
Registered
Joined
·
473 Posts
I put in brand new BOSH O2 sensors 5 months ago(still under warranty) to get rid of the code and now it's back..and my reader won't erase it..so I'm thinking it's a fuse..because you can reset a fuse..
Welcome to the Forum, from Cave Creek AZ!
 

·
The beast from Brazil
Joined
·
8,310 Posts
Which code(s) do you get?
 
1 - 16 of 16 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top