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drivewaylemonade 02-25-2013 12:41 PM

O2 signal voltage with sensor unplugged..?
At my wit's end with this thing. Bank 2 sensor 1 has a voltage of 1v even with the sensor unplugged. Have a scanner with live data. My fuel trim for both banks sits at 0 most of the time. Have seen bank 2 drop to -33.5. Jeep barely runs when this happens. Serious driveability issues when this occurs, sputtering, rough idle, lack of power when driving. If driving when this happens, flooring the gas pedal, causing a downshift cures it. For a short time. O2 sensor reading is constant 1 volt, plugged in, or not. Supply voltage is 4 volts. Driveability issues only occur when fuel trim drops off. Thought about TPS, but it reacted very smooth and linear when tested. New copper plugs, new air filter. PCM maybe? Any ideas? Just bought it last week. 70k miles on it. 4.7, pulls like a freight train when running well... :giveup:

Frango100 02-25-2013 04:07 PM

Re: O2 signal voltage with sensor unplugged..?
When you accelerate, the fuel control goes out of closed loop (so doesnīt use the 02 sensors anymore). The O2 sensor reading should fluctuate all the time. Not sure what the reading should be with the sensor disconnected. About which supply voltage of 4 V are you talking? The O2 sensors only have a 12 V input for the heater element, but there is no other power input to them. They in fact make their own power ( 0-1 V)depending on the amount of oxygen passing by.
The check engine light is not on and also no fault codes set?

drivewaylemonade 02-25-2013 05:21 PM

Re: O2 signal voltage with sensor unplugged..?
Check engine light is on. P0152. B2 S1 high voltage. That's why I put the scan tool on it. With the sensor unplugged the scan tool was still showing a signal voltage of 1v. That was when I put my multimeter to work. At the PCM end of the connector I have one prong with 12-14 volts, one with 4.0 volts, and the other two were direct to ground. I have also noticed that sometimes at idle my spark will vary from 14-12 degrees to 0 degrees. Make any sense to you..? Just scratching my head here.

Frango100 02-25-2013 05:45 PM

Re: O2 signal voltage with sensor unplugged..?
Did you measure on the connector where the O2 sensor connects to?
The 12 V must be the power for the sensor heater. But the 4 V should not be there i think. Did you already check the wire bundle for any shaving? When you remove connector C1 from the PCM, is then the 4 V gone or still there? Could maybe also be an internal PCM problem.

drivewaylemonade 02-26-2013 05:09 PM

Re: O2 signal voltage with sensor unplugged..?
Okay. So here's what happened today. Cleaned the IAC. Was fairly clean to begin with. Installed a new TPS. Checked all underhood fuses and relays. Checked connections at PCM. Battery was unhooked for about 1.5 hours. Decided to go for coffee to check things out and this is what happened: only have second and third gear. And reverse. And these codes popped up... P1768- relay always off(relays are stuck open), P1781-pressure switch circuit: OD, P1733- 4C pressure switch check, P1732- UD pressure switch check, P1734- 2C pressure switch check, and of course P0152- circuit high voltage bank 2 sensor 1. I miss my Mountaineer...

Frango100 02-26-2013 06:47 PM

Re: O2 signal voltage with sensor unplugged..?
Did you try to erase the codes first?
Did you mess with the TCM relay in the PDC and did you recheck all fuses again after this happened?

drivewaylemonade 02-26-2013 08:11 PM

Re: O2 signal voltage with sensor unplugged..?
The codes weren't there before I unhooked the battery. I didn't know anything until I pulled out of the driveway stuck in third gear. I checked and double checked every fuse and relay in it. I even switched the TCR and ASD relays to eliminate that. It's cold and dark out there now, and I need to be to work in the morning, so I'll be Powerglidin to Timmies tomorrow. Unless the ASD is the first problem. Hmm... :sleepy:

Frango100 02-26-2013 09:31 PM

Re: O2 signal voltage with sensor unplugged..?
The ASD should be ok, otherwise the engine wouldnīt even start.
For some reason the TCM doesnīt get power (seems to be the relay) and for that reason the tranny is in limp mode.
I would recheck the connectors which you removed before to see if they are well inserted and if no pins where bent.
Also check if the connector pins for the transmission relay are not pushed away (not sure if possible, but you never know.

drivewaylemonade 02-28-2013 02:11 PM

Re: O2 signal voltage with sensor unplugged..?
Spent the better part of another day under the hood. Pulled all the connectors, fuses, relays, PCM and TCM, hell, I even pulled the PDC. Pulled and twisted on the harness, sprayed everything with contact cleaner, and put it back together. Transmission seems fine. Has all forward gears, and overdrive again. Shifts are a little soft but it'll learn how I like them. Electrical gremlins are the worst kind. Now... To get that O2 sensor thing figured out. Thanks for your input, Frango. Gave me a place to start. :thumbsup:

Frango100 02-28-2013 06:49 PM

Re: O2 signal voltage with sensor unplugged..?
I have found some trouble shooting tips on the net which i will share with you, maybe it can help. The constant 1 V reading from the O2 sensor seems to be the sensor itself, but the 4 V from the PCM seems to be too high. Did you check the wiring if it didnīt touch the hot exhaust somewhere and is making a (partially)short. But ok, here comes the info i found::

02 Sensor Circuit High Voltage (Bank 2 Sensor 1)
What does that mean?

The o2 (oxygen) sensors basically measure oxygen content in the exhaust. The PCM (powertrain control module) then uses this information to regulate fuel injector pulse. The o2 sensors are very important to proper operation of the engine. Problems with them can cause the PCM to add or take away too much fuel based on the faulty o2 sensor voltage.
A P0152 code refers to the Bank 2, sensor 1, o2 sensor. (Bank 1 would contain cylinder 1 and bank 2 is the opposite bank. Bank 2 doesn't necessarily contain cylinder 2.) "Bank 2" refers to the side of the exhaust that DOES NOT contain cylinder number 1 and "Sensor 1" indicates that it is the pre-cat sensor, or forward(first) sensor on that bank. It is a four wire sensor. The PCM supplies a ground circuit and a reference voltage of about .5 volts on another circuit. Also for the o2 heater there is a battery voltage supply wire and another ground circuit for that. The o2 sensor heater allows the o2 sensor to warm up faster, thus achieving closed loop in less time than it would normally take for the exhaust to warm the sensor up to operating temperature.
The O2 sensor varies the supplied reference voltage based on oxygen content in the exhaust. It is capable of varying from .1 to .9 volts, .1 indicating lean exhaust and .9 indicating rich exhaust. NOTE: A condensed explanation of fuel trims: If the o2 sensor indicates that the oxygen voltage reading is .9 volts or high, the PCM interprets this as a rich condition in the exhaust and as a result decreases the amount of fuel entering the engine by shortening injector "on time". The STFT (short term fuel trims) would reflect this change. The opposite would occur when the PCM sees a lean condition. The PCM would add fuel which would be indicated by a single digit positive STFT reading. On a normal engine the front o2 sensors switch rapidly back and forth two or three times per second and the STFT would shift positive and negative single digits to add and remove fuel to compensate at a similar rate. This little "dance" goes on to keep the air/fuel ratio at it's optimal level. Short term fuel trims or STFT reflect immediate changes in fuel injector "on-time" while long term fuel trims or LTFT reflect changes in fuel over a longer period of time. If your STFT or LTFT readings are in the positive double digits (ten or above), this indicates the fuel system has been adding an abnormal amount of fuel than is necessary to keep the proper air/fuel ratio. It may be overcompentsating for a vacuum leak or a stuck lean o2 sensor, etc. The opposite would be true if the fuel trim readings are in the negative double digits. It would indicate that the fuel system has been taking away excessive amounts of fuel, perhaps to compensate for leaking injectors or a stuck rich o2 sensor, etc. So when experiencing o2 related issues, reading your fuel trims can indicate what the PCM has been doing over the long term and short term with regard to fuel.
This code indicates that the o2 sensor was stuck too high or in the rich position. The PCM monitors this voltage and if it determines that the voltage is too high out of range for too long, P0152 may set.


Symptoms may include:
  • MIL (Malfunction Indicator Lamp) illumination
  • Engine may run very rough
  • Engine may be running lean or rich depending on if the o2 sensor is reading correctly or incorrectly
  • Lack of power
  • Increased fuel consumption

Potential causes of an P0152 code include:
  • Bad bank 2, 1 o2 sensor incorrectly reading rich condition
  • Engine running rich and o2 sensor Correctly reading rich condition
  • Signal shorted to voltage in harness
  • Wiring harness damage/melted due to contact with exhaust components
  • Vacuum leak (make have lean codes (P0171, P0174) present with it)
  • Leaking injectors
  • Bad fuel pressure regulator
  • Bad PCM
Possible Solutions

If you have any lean or rich codes associated with this code, focus on fixing these first because these can cause the o2 sensor voltage readings to appear to be faulty when they are in fact only reading correctly.
So, with the engine running at operating temperature, use a scan tool to observe the Bank 2,1 o2 sensor voltage reading. Is it high? If so, look at the long term and short term fuel trim readings. The fuel trims are affected by the o2 sensors as noted above. If the LTFT reading for that bank is indicating negative double digits (PCM trying to take away fuel to compensate for problem) try inducing a vacuum leak to see if the sensor voltage then goes lean and the fuel trims increase. If the o2 sensor responds, suspect a problem with the engine, not the sensor. There may be other engine codes to help you.
If the o2 sensor reading remains high (0.9 volts or above) and won't respond then shut off engine. With KOEO (Key on engine off) disconnect the o2 sensor and look for signs of corrosion or water intrustion. Repair as necessary. The voltage reading should now be about 0.5 volts. If so, replace the o2 sensor, it's shorted internally.
If after unplugging the o2 sensor the voltage reading on the scan tool doesn't change, then suspect wiring problems. Inspect the harness and look for any melted wires or anywhere that the o2 sensor harness is making contact with the exhaust components. If you are unsure, you can check for continuity of all four wires between the sensor and the PCM with an ohmmeter. Any resistance at all indicates a problem. Repair as necessary.

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