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My scan says heater performance bank1 sensor 2. I checked the heater wires( 2 black) and got 9.5 ohms resistance. I checked signal wires and never got over 399mv of DC current with car warmed up. It is a stock 1999 5.7l. I thought anything over 2 ohms was good on the heater side. I was expecting 450mv or more on signal so 399mv appears low. Could weak signal throw a heater malfunction code? Thanks for any advice I can get.
Last edited by Rocky11; Mar 16, 2025 at 09:16 PM.
Reason: Add to title
With the engine warmed up and engine running the sensor 2 downstream O2’s usually hover about 600-700mv’s are is fairly constant…3.5 to 14 ohms is good on the heater circuit…have you checked for the ignition feed and ground on the heater circuit wires ??…when the engine is cool you should see a 450mv bias voltage on the signal side with your scan tool with fuse 15 removed …if you remove fuse 15 and with the scan tool hooked up turn the ignition on and you will see the 450mv bias..now install fuse 15 and you should see the signal circuit voltage drop from 450 to below 200 mv’s in about 30 seconds…this tells you that the heater circuit is functional…anytime the ignition is on the heater circuit is working so you won’t see that bias voltage…that is why we remove fuse 15…brown is ignition feed and black is ground…BTW an exhaust leak upstream of the rear O2 sensor will drive the sensor voltage low because of that unmetered air causing a lean condition…if the upstream is lean the downstream should be lean also.
With the engine warmed up and engine running the sensor 2 downstream O2’s usually hover about 600-700mv’s are is fairly constant…3.5 to 14 ohms is good on the heater circuit…have you checked for the ignition feed and ground on the heater circuit wires ??…when the engine is cool you should see a 450mv bias voltage on the signal side with your scan tool with fuse 15 removed …if you remove fuse 15 and with the scan tool hooked up turn the ignition on and you will see the 450mv bias..now install fuse 15 and you should see the signal circuit voltage drop from 450 to below 200 mv’s in about 30 seconds…this tells you that the heater circuit is functional…anytime the ignition is on the heater circuit is working so you won’t see that bias voltage…that is why we remove fuse 15…brown is ignition feed and black is ground…BTW an exhaust leak upstream of the rear O2 sensor will drive the sensor voltage low because of that unmetered air causing a lean condition…if the upstream is lean the downstream should be lean also.
Thanks for the info. If I understand correctly, I hook my scanner, pull fuse 15 and turn the ignition on. If the current drops to200-300mv, the heater circuit is good. I guess if it doesn't, I need a new sensor. I don't see or hear any exhaust leak but I'll compare it to sensor 1 to check.
I’d pull the fuse first and then connect your scan tool and turn the key on…if the engine has been sitting for a while you should see 450mv’s…now insert the fuse and you should see the voltage drop below 200 mv’s…before condemning the sensor you want to make you have good power and ground on the heater circuit…I check power and ground with a bulb that draws about 1-2 amps…if I place the bulb on the power and ground it should be bright…resistance testing is not the correct way to check a ground…I can’t remember if the picture below was the amperage of the front or rear O2 heater…1.55 amps.
P0141 O2 sensor code
