Hello everyone,

I recently got my truck (2000 Ram 1500, 5.9L, 4x2, CA emissions) up and running after many many months of on and off again work on it but had several codes pop up: P0132 (confirmed), P0135 (pending), and P0138 (pending).

Before putting the front end of the engine in and while I had ample access to the wiring harness I tested all sensors, including the four O2 sensors for continuity and voltage. It appeared that all of the connections to the sensor's connector and back to the PCM were not shorted anywhere and all had continuity and a resistance of 0.2 ohms. The orange/black wire (I believe this is the 5v power wire) was measured at 4.11 V on sensor 1 of bank 1, and 4.25 V on sensor 2 of bank 1 with the key in and the engine off, so, a bit low but I'm not sure what would cause this as the battery had sufficient voltage and had just been fully charged at Autozone.

I found another website that suggested several ways to diagnose the issue. I swapped sensors from bank to bank 2, as if the sensors are bad then I'd get an error code for the bank 2 sensors, but oddly enough, I swapped them and the problem completely disappeared for ~40 miles. I didn't clear the code, upon startup it just went away. On my way back home I checked the live data on my scan tool and this is what showed up. It appears that sensor 1 on bank 1 is functioning normally (bouncing rapidly between 0.12V and 0.92V) and sensor 2 on bank 1 may not be? Once I got home I restarted the truck and idled for a while and noticed that now sensor 2 on bank 1 was almost constantly at a 0.5V reading, and I unplugged the vacuum line leading from the PCV valve to the intake manifold to try to force a lean condition and this is what the sensors read.

I'm really quite confused on how to proceed with diagnostics and don't want to just buy a ton of parts and try swapping them out. Everything in the engine compartment on this vehicle except the brake booster, master cylinder, wiring harness, and PCM are brand new or refurbished, and the catalytic converter was purchased brand new ($2000, I hate California...). Some other posts on here said that it could be a fuel pressure/leaking injector issue, and while I did originally have a leaky #5 injector I ripped off the fuel rail, replaced the O-rings and haven't had an issue since. Additionally I have a new fuel pump/regulator unit in the tank and verified that the fuel pressure is within the correct operational range. All of my vacuum lines are brand new and the only current change from stock is the climate control is capped off as I'm working on the interior and damaged the line leading through the firewall. Something in my mind keeps going back to the wiring harness, but as I stated before I checked all of the wires for continuity, and, when I first purchased the truck I ripped the harness out, inspected each wire and re-wrapped it in several layers of Tesa wiring harness tape and verified that none of the wires have melted to and shorted on the manifold or cats.

One other thing that keeps nagging me in my mind is the breather unit that came with my aftermarket valve covers. It doesn't have the typical vents at the bottom like other breathers, and has a one way valve similar to a PCV. I'm starting to wonder if I in fact I was sent a PCV valve by mistake with my valve covers and unknowingly have installed two PCV valves. This is the PCV valve installed on the driver's side of the engine. Could the lack of a breather unit and the installation of an additional PCV valve that goes to the air cleaner cause this issue?

I appreciate any input. Thanks!

 

Sensor 2 being fairly steady is normal. It is reading oxygen content of the exhaust AFTER the cat..... so, there really shouldn't be much variance there. The two latter codes deal with the heater circuit, either no voltage, or, too high of a current draw. Could be a bad sensor, or, a short to ground on the voltage supply side.

 

I swapped sensors from bank 1 to bank 2 and vice versa, so if the sensor was in fact bad wouldn't I be getting a code for the upstream bank 1 sensor then?

How would I go about ensuring there isn't a short to ground on the voltage supply side?

 

Test continuity to ground on the heater circuit voltage wire.

 

So it turns out I do in fact a short to ground in potentially more than one location. While I'm unsure about each of the following connections, some are obviously a short somewhere in the harness, I just haven't had time to track each wire down in the service manual to confirm it shouldn't be grounded on anything other than the #4 sensor ground on C1 on the PCM.

Connectors to the PCM I had the following wires going to ground:
C1: #2 (Fused ignition switch), #4 (Sensor ground), #6 (Park/neutral position signal), #7 (Ignition coil), #15 (Intake air temperature sensor signal), # 16( engine coolant temperature sensor signal), # 22 (Fuse B+), #31 (various grounds), #32 (various grounds)
C2: None
C3: #1 (A/C compressor clutch relay), #2 (TBD), #3 (Auto shut down relay control), #4 (Speed control vacuum solenoid control), #5 (Speed control vent solenoid control), #8 (Bank 1/Sensor 1 O2 Heater Signal), #9 (O2 Sensor Downstream Relay Control), #11 (Speed control supply signal), #19 (Fuel pump relay control), #20 (Evap emission control solenoid), #24 (Brake switch sensor signal), #27 (SCI transmit), #28 (CCD Bus -), #29 (SCI receive), #30 (CCD bus +)

Looks like I need to splice in a new set of cables for C3 #8 and #9 at least. I'm obviously not an expert but it feels like there shouldn't be that many wires going to ground.

 

P0132 O2 Sensor 1/1 Circuit Voltage High
P0135 O2 Sensor 1/1 Heater Failure
P0138 O2 Sensor 1/2 Circuit Voltage High
How old are the sensors? Are you checking the voltages(return to pcm) in closed loop? You have no codes for a short. 02's get power from the sad relay and a constant ground. Check both at the plug for the 02.

 

The sensors are all brand new. I purchased them in 2022 but they sat in their boxes in the garage until recently.

I've only checked the voltages with the key in and engine off. Checking the voltages in closed loop would require the engine to get to operating temperature correct? I have the CA emissions cats and exhaust so it's rather difficult to do that with the engine on without burning the hell out of my arms.

As a side note, when I swapped the sensors I noticed a lot of carbon buildup on them. At the time I figured it was just from the first few times I started the engine up and it was running a bit rough. But now that I recall I had a leaky #5 injector which has since been fixed. Could this stem from a failing injector?

Thanks for the reply!

 

What brand sensors are they?

 

They are Walker Products #25024943 and #25024942. I know people on here like the NGK/NTK ones but I purchased these prior to knowing that those are essentially the end all be all. They are the second set of Walker ones I've purchased though, as previously I was chasing down another demon in this machine and thought it might've been the O2s. I did test the resistance of the built in O2 sensor heater and all of the measured about 4.5 ohms which to my knowledge is acceptable when testing at room temperature with the sensor unplugged.

 

Would you recommend buying NGK/NTK sensors and seeing if that solves the issue?