Hoping I can get some advice. let me know if I am posting in the wrong place, but I just picked up a 97 xlt 4x4. The only issue I am having is that it is running rich. I am getting codes related to the HEGO system. P0141, 0155, 0135, 1132, and 1152. I was hoping that it may have been the fuse for the system considering that it seems unlikely for all O2 sensors to fail at the same time, but the fuse looked fine. I replaced it with a new one just in case, but it didnt fix the issue. I did buy the truck with these codes so I don't know how long it has been running like this. The truck does have a brand new catalytic converter so it is possible that it has been allowed to run rich for a while. I am considering buying all new O2 sensors but wondering if there is anything I should attempt before I start throwing parts at it. I cleaned the MAF, Throttle body and IAC but havent seen any change.

 

My first guess is a wiring problem.

If the transmission or clutch has been replaced, a common problem is the wiring to the sensors gets pinched between the block and bell housing and cuts the wires when being re-assembled.

 

+1 ^^^^

P0135 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
P0155 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
P0141 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)

"Circuit" code

Inside each O2 sensor is a separate heater, the heater part gets 12volts with key on and then Computer Grounds it to activate heater
The Three O2 sensors share that one 12volt wire and fuse(fuse #3 15amp in engine bay fuse box)
Each heater has its own ground wire back to the computer, with key on and computer booting up the computer will "see" 12volts on each O2's Ground wire(heater is just a coil of wire, so 12v passes thru it)
If computer doesn't "see" 12v on O2 bank 1, sensor 1's ground wire it would set P0135 code
You are seeing same code description for all three O2 sensors
Since this is a shared 12v source then 12volt source is not working
In a 1997 4.0l a Light Blue/orange stripe wire is the 12v wire at each O2 sensor

Unplug any O2 sensor's 4 wire connector and test light blue/orange wire, should have 12v key ON
Work your way back thru the wiring until you find the break

Before you start, pull out #3 fuse and turn key ON, test fuse connections, one should show 12v, if not then thats where to start, no 12v at the fuse itself
If you see 12v then put fuse back in and test for 12v at closest O2 sensor

Just FYI
"Rich" codes are caused by No Heaters, so ignore them until heaters are all working

 

Thanks so much for the responses, only just saw them now. Been focused on other elements of the truck for a while. I am back to trying to get the o2 sensors up and running. I just tested fuse number 3, and I have 12v there. Later today I will check at the connectors. If I understand your responses correctly, if I find a sensor that is not getting 12v, my problem will be in the wiring somewhere between the sensors and the computer? This is my first time troubleshooting any significant wiring issues so I just want to make sure I am going about this correctly. Truck has been running well but seems to be stuck running in "open-loop" without the sensors operating correctly.

Thanks!

 

Yes, "Closed Loop" means O2 sensors are working and engine temp is above 140degF(no choke)

1 wire on each of the 4 wire O2 connectors should have 12volts as soon as key is turned on
In 1997 should be a Light Blue/orange stripe wire on each, all 3 O2s use the same wire just daisy chain from one to the next
So for all 3 O2s to show "heater code", then fuse or wire from fuse is bad