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sprinkles08, ASE Certified Technician
Category: Jeep
Satisfied Customers: 22826
Experience:  Chrysler/Dodge/Jeep Master Certified, ASE Master and Advanced Certified, Trans and Hybrid Specialist
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Low voltage period of time circuit. 05 Jeep Wrangler 4.0. 4

Customer Question

Low voltage for extended period of time for heater circuit . 05 Jeep Wrangler 4.0 .
4 codes for all four o2 sensors. Check engine light is on . Jeep runs fine .
P0031 heater circuit low b1-s1
P0031 heater circuit low b1-s2
Poo51 heater relay circuit low b2-s1
P0057 heater relay Circuit low b2-s2
Submitted: 1 year ago.
Category: Jeep
Expert:  sprinkles08 replied 1 year ago.

Hello and welcome to JustAnswer!

You either have multiple failed oxygen sensors or a wiring issue. It wouldn't be likely for four sensors to fail at once although a sensor is the most likely cause for an oxygen sensor code. If all four codes started setting at once it's more likely to be a loss of ground to the heaters.

Has anything been done to try to repair the problem?

Customer: replied 1 year ago.
I agree I don't think all four went down at once . I don't think it's an o2 sensor at all . I haven't replaced any parts but I've been trying to use a multimeter to check for voltage , ohms and continuity . A shared common ground seems likely issue or maybe pcm . I've taken reading from all the pins for the wires on each connector attached to the harness for the o2 sensors . I cldnt tell which two was for heater circuit so I took readings from all . From what I read if too much resistance is on ground then it cld throw these codes and likely given they all r coding out
Customer: replied 1 year ago.
Here's the reading I got . Again two of the wires reading per sensor are likely not needed as we only need reading from heater circuit right ?bank1/sensor 1
brown/w lightgreen .798 v and 0 ohm
blk/ w light green 1.7 v and 16.7 ohm (only one to beep on contiunity)
blue /w light blue 4.17 v and 11.9 ohm
brown /w blueish green ? 2.4 v and 11.4 ohm
bank2 sensor1
blk / w green 1.7 v and 16.2 ohms ( only one to beep on continuity)
brown w/ violet .958 v and 32 ohm
blue w/ light green 4.25 v and 11.9 ohm
br w/ green 2.4 v and 11.9 ohm
bank1 sensor 2
blk w/ blue 1.7 v and 11.7 ohm (only to be on continuity)
brown w/ white .96 v and 31 ohms
blue w/ light green 4.1 v and 10.7 ohms
blue wire 2.4 v and 13 ohm
bank 2 sensor 2
brown wire 4.2 v and 10.95 ohm
br w/ white 1.6 v and 0 ohm
blk w/ blue 3v and 29 ohm (only to beep on continuity)
blue wire 2.4 v and 11.7 ohm
Expert:  sprinkles08 replied 1 year ago.

Do you have a headlamp bulb and a couple jumper wires?

Customer: replied 1 year ago.
No. Unless I make something . Did u receive the reading I took ? Do they tell u anything ?
Expert:  sprinkles08 replied 1 year ago.

I did take a look at your measurements but the accurate way to test the heater ground circuits is a load test with a bulb. A circuit can show zero ohms but not be able to carry enough current to operate a load. What you'll want to do is rig a bulb up to work as a high current draw test light and then test the black/light blue and black/light green ground wires. If the bulb is dim or doesn't light then you have a ground issue, if it lights brightly then you have a sensor, heater driver circuit or PCM issue.

Customer: replied 1 year ago.
Ok and does it matter if I'm probing the connector pins for those wires at same time or one at a time with my other jumper on a good ground ? Also for the voltage side ,if the heater circuit is only on briefly then is it possible I may not b getting to the connector in time to check the voltage coming in before the Pam turns it off ?
Expert:  sprinkles08 replied 1 year ago.

You'll connect one jumper wire to battery positive, the other end to a terminal on the bulb. Another jumper wire will go from the other bulb terminal to the wire you're testing, which will be the ground wire at each sensor.

The heater drivers aren't something that you can test at least without a scan tool to actuate them to full duty cycle. What needs to be done is test the ground circuit, the driver circuits can be load tested, and the resistance of the heater elements themselves can be tested.

Customer: replied 1 year ago.
Ok so I've ohmed the sensor its self reading 3-4 ohms each .so I thought that meant they were ok . Hell idk . I'll just have to try the ground light thing . I'll go at lunch and try to buy a setup at Autozone . If this don't work I guess I'll take my chances with an auto shop . Hate that though tricking problems sound expensive :) . Thank you for your time
Customer: replied 1 year ago.
Will the heater circuit for the o2 sensor have 12v at all times the key is on or only at certain times . Hard to check for voltage if the person only sends at certain times
Expert:  sprinkles08 replied 1 year ago.

Element resistance is 2-30 ohms so 3 ohms would be within spec marginally if they were tested at room temperature.

The heaters are duty cycled based on driving conditions and element temperature, calculated by circuit resistance. The only way to test the heater drivers is with a scan tool to actuate them.