Oxygen sensor problems
CF Veteran
Joined: Aug 2010
Posts: 8,357
Likes: 103
From: Canton, MI
Year: 1999
Model: Cherokee
Engine: 4.0
Questions:
1. What brand (make) O2S's did you install? Were they Universal Fit (where you had to splice in the wires), or were they Exact Fit (where the O2S's had a connector on them that matched the body harness connectors)?
2. Did you, in fact, put a NEW fuse in the F17 slot?
Try this:
If you are getting battery voltage at F17 bus side of the fuse slot (A21) but not at relay pin sockets 11 and 16 try this:
Remove fuse F17, remove the Upstream O2S Heater relay, install a jumper from the relay pin socket C11 to ground (battery (-) post); then using your voltmeter, read between the pin cavities A21 and A22 of fuse F17. You should read battery voltage. If not, the wire(s) you see in the diagram that go from the fuse to the relays may be smoked. You would need to diassembly the PDC to gain access to its bottom to check these wires. If you do get battery voltage the referenced wires are intact.
Please answer the above questions.
1. What brand (make) O2S's did you install? Were they Universal Fit (where you had to splice in the wires), or were they Exact Fit (where the O2S's had a connector on them that matched the body harness connectors)?
2. Did you, in fact, put a NEW fuse in the F17 slot?
Try this:
If you are getting battery voltage at F17 bus side of the fuse slot (A21) but not at relay pin sockets 11 and 16 try this:
Remove fuse F17, remove the Upstream O2S Heater relay, install a jumper from the relay pin socket C11 to ground (battery (-) post); then using your voltmeter, read between the pin cavities A21 and A22 of fuse F17. You should read battery voltage. If not, the wire(s) you see in the diagram that go from the fuse to the relays may be smoked. You would need to diassembly the PDC to gain access to its bottom to check these wires. If you do get battery voltage the referenced wires are intact.
Please answer the above questions.
Thread Starter
Junior Member
Joined: Dec 2008
Posts: 75
Likes: 0
From: Michigan City,IN
Year: 2000
Model: Cherokee
Engine: 4.0L
Thread Starter
Junior Member
Joined: Dec 2008
Posts: 75
Likes: 0
From: Michigan City,IN
Year: 2000
Model: Cherokee
Engine: 4.0L
WOW!!!! I must be the biggest dumb***!! I have been messing with the wrong 20a fuse i put the correct fuse in but I still do not have bat voltage at the O2 plug(vehicle side)
I do have power at the relays correctly now
I do have power at the relays correctly now
CF Veteran
Joined: Aug 2010
Posts: 8,357
Likes: 103
From: Canton, MI
Year: 1999
Model: Cherokee
Engine: 4.0
While you have the relays out, read voltge between pin socket C20 and ground with the key OFF. You should see between .02 and .125 volts. This is the PCM/CCD Bus idle voltage. Do the same on the other relay, pin socket C15 to ground. If your read zero volts, turn the key to RUN then back to OFF, and try it again. If you still get zero volts, there's an open from the relay to the PCM, or the PCM relay driver(s) are dead.
