Hi there.

So I've picked up a new Cherokee, my third - 2001, 4wd, i6, Canadian (like the Californian one, 4 o2 sensors). Everything runs great, but there are some codes...

Preface: the previous owner removed all the catalytic converters. I have only three bungs for o2 sensors - two "upstream" and one "downstream" - four are connected. I will reinstall the stock cats as soon as I can. The problems do seem unrelated...

I've got codes:

PO135
PO141
PO155
P0161

All four heater circuits for the o2 sensors = bank 1/1, 1/2, 2/1, 2/2. Looking for answers as to what I have missed, or possibly the idea that the PCM is faulty. My troubleshooting so far....

-12v to fuse 17 (new fuse 20A) ✓
-voltage from junction block (new fuse 15A) ✓
-12v to downstream relay (c16) ✓
-12v to upstream relay (c11) ✓

Here we get no voltage going to connection c107. If I jump c11 to 12 and/or c16 to 17 I get the 12v to the sensors no problem, system seems to function fine.

-new (tested) relays ✓
-new (NGK/NTK - not the problem, but might as well get the right ones) o2 sensors ✓
-continuity from upstream relay (c12) to c3 of PCM (pin 8) ✓
-continuity from downstream relay (c20) to c3 of PCM (pin 9) ✓

Voltage from both PCM relay controls to relays reads 0.06. I believe this is in spec (0.02 - 0.125 - maybe this can be disputed, not sure on this)

Grounds in the circuit all read 0.2ohms.

I have researched endlessly, read through CCKen's posts (and many others), but haven't found a solution yet. I've looked in the FSM, redrawn the circuit drawings to get a better understanding... I've checked all the wiring, everywhere seems to connect happily, it's just that the relays don't seem to be activating to allow voltage through.

What am I missing? I've checked the grounds for everything in the circuit. I'm open to having failed in my troubleshooting so far, and am open to suggestions. Or if I should give in to a pro.

Thanks,
Joe.

 

Did you check for voltage at pins C13 and C16 at the O2 relays? Sorry but it's unclear to me by your description above. They are fed from Fuse 10 in the JB (15a). They connect through a splice (S159) and other connectors (C201, C100). The PCM then grounds the relays.

When you checked continuity, did you back probe the pins or did you remove the connector? Carefully look at the pins, both sides for any corrosion.

When you tested the relays, did you check for continuity across the O2 relays contacts while applying 12 volts across the coil?

 

Also, what other codes are you getting? I imagine more than just those 4. Since the upstream are located in the manifolds, and the down stream normally, just aft of the 2 cats, where is the downstream one located? Was the harness extended to some other location? Is the 4th one just dangling or tied off somewhere?

 

Howdy,

Thanks for coming out. C13 and C16 are getting voltage, yes. For continuity I removed connectors, they are all free of corrosion.

I'm only getting these codes, no others. The upstream sensors are roughly where they should be originally. The one downstream that's on the exhaust is also close to original location, The harness wasn't extrended.. The other downstream is plugged in, but zipped tied out of the way.

 

Well, with no cats and one O2 hanging out in the "breeze" I'm confused about why you don't have more codes, like cat efficiency codes.

Can you see part number on the PCM?

 

You are certainly right, it is weird that it doesn't have more codes. I guess my real hope was to at least get the upstream sensors working, maybe improving my gas mileage some - I'm driving across the country in a week.

Part number is P56041 801 AD