View Poll Results: Should I rewire the 02 sensor heater circuit to avoid pesky FF44 codes & its problems
Yes! That's a brilliant Idea. In fact, it's *MY* idea. I should get all the credit!
0
0%
I don't know.... This whole idea makes my head hurt.
0
0%
What? Why don't you eat arsenic and cyanide while you're at it. That idea is just nuts!
0
0%
Multiple Choice Poll. Voters: 1. You may not vote on this poll
H02S & Pesky FF44 -- My Plan to rewire 02 sensor heater circuit - Pls comment
#1
07-06-2017, 01:25 PM
H02S & Pesky FF44 -- How to trouble shoot on a 93 XJ-S AJ6 4.0L engine...
So,
I've got an FF44 code, and because of it, my car goes into a "preprogrammed" mode where it runs in open loop mode and runs rich, which causes me to fail emissions inspection.
As a help to all, I'll post what I found and what I learned -- thanks to the forum and resources that I found because of the forum.
Wiring Diagrams for the 1993 XJS are here:
1993 XJ-S Electrical Wiring Diagram
And the relevant portions of the "AJ6 4.0L Engine Management System /OBD I diagnostic guide" are attached as a PDF.
I had posted an idea about cutting the two heater wires in the harness (blue w/ red circles for +12V, Black for ground) and simply
running the side that goes to the 02 sensor to a switched +12V source with an inline fuse added, and running the ground wire to a good, underhood ground.
I plan to do that as a quick work around to pass inspection, but, @warrjon provided me with information on the wiring, so that I can eventually *correctly* trouble shoot the problem.
With the wiring diagram (link above) and the relevant portions of the Diagnostic Guide (attached) it should help you diagnose FF44 errors like a pro!!!
The wiring diagram shows a little more detail than the diagnostic guide.
Either one is right and the other is wrong, or they are both right, but the diagnostic guide simplies things. Last option... I think that Jag made changes to the XJS in the middle of the 1993 Model Year, so maybe one diagram is pre-changes and the other is post. I'm not sure.
None-the-less, in my case, the underhood harness had melted, shorting all 3 of the 02 sensor wires together, so I'll skip the early diagnosis steps related to fuel pressure and other items... my problem is almost certainly making sure that the heater circuit gets power, because the short may have melted or burned something out.
Here's a quick summary of how the jag powers the heater wire on the 02 sensor (at least in the 1993 XJS convertible).
Starting in the trunk on the right hand side is a relay for the fuel pump. Pin 87 of that relay has a blue wire with red marks on it (UR = blUe w/ Red).
This wire(blue with red) gets +12V applied by the fuel pump relay when the car is in the run position.
The wire then takes the following path to provide +12V to the heating circuit of the 02 sensor.
From the fuel pump relay (pin 87), the wire runs
to a harness related to the fuel pump. All harness and splices are labeled.
This harness is RH104-2 which stands for pin 2 of harness 104 on the rear right hand side of the car.
BUT, before that connection, the feed to power the O2 sensor is spliced off to another wire that is the the same color (blUe with Red or UR). The splice is labeled RHS18. RH is the location (right hand rear), S is for Spice, and 18 is the number of the splice.
From the splice, the wire (same color) goes to connector RH160-10 (Pin 10 of connector 160 in the rear right hand side) and it continues from there.
Here's the whole path (according to the wiring guide linked to above)
Fuel Pump Relay Pin 87 - Rear Right hand side blUe wire with Red circles (UR)
to
Splice RHS18 (still UR color -- Right hand rear splice number 18)
to
RH160 - 10 (still UR color -- Right hand rear connector 160 pin 10)
to
LI135-2 (still UR color -- xxxxx location connector 135 pin 2)
to
LI122-1 (still UR color -- xxxx location connector 122 pin 1).
So with this information I can trace the wire with a digital multimeter checking for continuity,
and for improper shorts to ground and/or open circuits, and I should be able to find out where the problem is.
I will start at the last connector under the hood, disconnect it and with the engine in the "ON" position and check for +12v on the blue w/red wire, and for a good ground on the on the black wire in the harness. If I don't find +12V, I'll (carefully) test it again with the engine running, just to be certain that the fuel pump relay (which powers the 02 heater wire) is actually on.
Based on what I find I can work back from there.
For now, to get the car to pass emissions, I just cut the harness wires, and power the 02 sensor heater directly by sending +12V through an in-line fuse to the blue w/ red wire leading to the 02 sensor, and ground the black wire that leads to the O2 sensor.
Once I confirm that this works, and pass emissions inspection, then I can go back and trace the wires on the factory harness to find out where the problem really is. I've read (even in the service manual) that it's not uncommon for the problem to be a poor ground.... but I'll take it step by step, and it could be one of many causes.
Hope this info helps others.
-Phil
I've got an FF44 code, and because of it, my car goes into a "preprogrammed" mode where it runs in open loop mode and runs rich, which causes me to fail emissions inspection.
As a help to all, I'll post what I found and what I learned -- thanks to the forum and resources that I found because of the forum.
Wiring Diagrams for the 1993 XJS are here:
1993 XJ-S Electrical Wiring Diagram
And the relevant portions of the "AJ6 4.0L Engine Management System /OBD I diagnostic guide" are attached as a PDF.
I had posted an idea about cutting the two heater wires in the harness (blue w/ red circles for +12V, Black for ground) and simply
running the side that goes to the 02 sensor to a switched +12V source with an inline fuse added, and running the ground wire to a good, underhood ground.
I plan to do that as a quick work around to pass inspection, but, @warrjon provided me with information on the wiring, so that I can eventually *correctly* trouble shoot the problem.
With the wiring diagram (link above) and the relevant portions of the Diagnostic Guide (attached) it should help you diagnose FF44 errors like a pro!!!
The wiring diagram shows a little more detail than the diagnostic guide.
Either one is right and the other is wrong, or they are both right, but the diagnostic guide simplies things. Last option... I think that Jag made changes to the XJS in the middle of the 1993 Model Year, so maybe one diagram is pre-changes and the other is post. I'm not sure.
None-the-less, in my case, the underhood harness had melted, shorting all 3 of the 02 sensor wires together, so I'll skip the early diagnosis steps related to fuel pressure and other items... my problem is almost certainly making sure that the heater circuit gets power, because the short may have melted or burned something out.
Here's a quick summary of how the jag powers the heater wire on the 02 sensor (at least in the 1993 XJS convertible).
Starting in the trunk on the right hand side is a relay for the fuel pump. Pin 87 of that relay has a blue wire with red marks on it (UR = blUe w/ Red).
This wire(blue with red) gets +12V applied by the fuel pump relay when the car is in the run position.
The wire then takes the following path to provide +12V to the heating circuit of the 02 sensor.
From the fuel pump relay (pin 87), the wire runs
to a harness related to the fuel pump. All harness and splices are labeled.
This harness is RH104-2 which stands for pin 2 of harness 104 on the rear right hand side of the car.
BUT, before that connection, the feed to power the O2 sensor is spliced off to another wire that is the the same color (blUe with Red or UR). The splice is labeled RHS18. RH is the location (right hand rear), S is for Spice, and 18 is the number of the splice.
From the splice, the wire (same color) goes to connector RH160-10 (Pin 10 of connector 160 in the rear right hand side) and it continues from there.
Here's the whole path (according to the wiring guide linked to above)
Fuel Pump Relay Pin 87 - Rear Right hand side blUe wire with Red circles (UR)
to
Splice RHS18 (still UR color -- Right hand rear splice number 18)
to
RH160 - 10 (still UR color -- Right hand rear connector 160 pin 10)
to
LI135-2 (still UR color -- xxxxx location connector 135 pin 2)
to
LI122-1 (still UR color -- xxxx location connector 122 pin 1).
So with this information I can trace the wire with a digital multimeter checking for continuity,
and for improper shorts to ground and/or open circuits, and I should be able to find out where the problem is.
I will start at the last connector under the hood, disconnect it and with the engine in the "ON" position and check for +12v on the blue w/red wire, and for a good ground on the on the black wire in the harness. If I don't find +12V, I'll (carefully) test it again with the engine running, just to be certain that the fuel pump relay (which powers the 02 heater wire) is actually on.
Based on what I find I can work back from there.
For now, to get the car to pass emissions, I just cut the harness wires, and power the 02 sensor heater directly by sending +12V through an in-line fuse to the blue w/ red wire leading to the 02 sensor, and ground the black wire that leads to the O2 sensor.
Once I confirm that this works, and pass emissions inspection, then I can go back and trace the wires on the factory harness to find out where the problem really is. I've read (even in the service manual) that it's not uncommon for the problem to be a poor ground.... but I'll take it step by step, and it could be one of many causes.
Hope this info helps others.
-Phil
Last edited by phil_xjs_conv; 07-07-2017 at 11:33 AM. Reason: Removed my question, and posted a solution, diagnostic guide and wiring schematics