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Today I had a new stereo and related accessories installed on my RX350 (2009 with 113K miles). About an hour after leaving the installation shop my dash popped up with the CEL, traction control and VSC warning lights. A scan revealed both P0031 (Bank 1, Sensor 1) and P0051 (Bank 2, Sensor 1) error codes indicating the "Heater Control Circuit Low." I reset the CEL's 3 times and within a mile or roughly 5 minutes of driving the lights will come back on with the same error codes. I understand the O2 sensors can fail and with my high mileage are likely overdue. I was surprised however that both banks would fail at the same time. Is it likely for both to fail at the same time? Could anything the stereo installer did have caused this to happen? From my online reading I am wondering if something happened to the ECM but I don't understand it well enough to know if that is something to explore. I appreciate any assistance. TIA, Todd
Today I had a new stereo and related accessories installed on my RX350 (2009 with 113K miles). About an hour after leaving the installation shop my dash popped up with the CEL, traction control and VSC warning lights. A scan revealed both P0031 (Bank 1, Sensor 1) and P0051 (Bank 2, Sensor 1) error codes indicating the "Heater Control Circuit Low." I reset the CEL's 3 times and within a mile or roughly 5 minutes of driving the lights will come back on with the same error codes. I understand the O2 sensors can fail and with my high mileage are likely overdue. I was surprised however that both banks would fail at the same time. Is it likely for both to fail at the same time? Could anything the stereo installer did have caused this to happen? From my online reading I am wondering if something happened to the ECM but I don't understand it well enough to know if that is something to explore. I appreciate any assistance. TIA, Todd
Could very well be more battery voltage if they left the doors open for any extended period of time that is very common. Do you buy chance have a battery charger or maintainer you can use overnight?
One code may be coincidence but two codes?
No way. Lol
If they put in a new stereo they may have pulled fuses or who knows what
Check out the other members post above first
Next, I'd go over their work with a fine toothed comb and check all the fuses and see if any are missing and if they did a power tap in the fuse box for the new deck and messed something up.
When in doubt, always check your work.
In this case, check the last guy's work. Lol
First off, these are not O2 sensors, they are A/F sensors, and are quite different. Looking at the wiring diagram, these 2 A/F sensors share the +B (12V plus, yellow wire) hot connection, then the yellow wire goes the the A/F relay. So I would suspect something with that relay, or the connections to it.
The grounds for the A/F relay are shared with the EFI relay, so if the car is running, they are likely ok. The hot to trigger the A/F relay violet wire, does indeed end up at a fuse as suggested above:
"Could very well be more battery voltage if they left the doors open for any extended period of time that is very common. Do you buy chance have a battery charger or maintainer you can use overnight?"
Thank you "Leeper" for the suggestion. Per your suggestion, I put the battery charger on and it immediately posted a battery full message. I set up maintainer mode and have it running now.
One code may be coincidence but two codes?
No way. Lol
If they put in a new stereo they may have pulled fuses or who knows what
Check out the other members post above first
Next, I'd go over their work with a fine toothed comb and check all the fuses and see if any are missing and if they did a power tap in the fuse box for the new deck and messed something up.
When in doubt, always check your work.
In this case, check the last guy's work. Lol
Thank you for the suggestion. I confirmed three fuses are installed and fine (EFI 1 & 2 plus A/F). I have removed the car stereo and begun the process of double checking their work. I am also going into the shop first thing this morning when the open.
"Could very well be more battery voltage if they left the doors open for any extended period of time that is very common. Do you buy chance have a battery charger or maintainer you can use overnight?"
Thank you "Leeper" for the suggestion. Per your suggestion, I put the battery charger on and it immediately posted a battery full message. I set up maintainer mode and have it running now.
Sorry confused your post with another - if when installing the battery they left the doors open, which they did, they likely drained a lot of pwoer from the battery adn ow voltage can often cause phantom CEL and other anomoloies. Put it on a maintainer overnight, check the voltage shuold read at least 12.4V sitting and 14.4V running. It is rare that an installer will pull a fuse when installing stereos, they (and I) just disconnect the battery leads however a mistake can lead to a blown fuse. By the sound of the faults it does not sound like an error installing just low voltage. Also if they disconencted your battery you'll need to reset the windows, rear hatch, sunroof, and the car will take a few miles to relearn your driving techniques as the ECM has been erased.
First off, these are not O2 sensors, they are A/F sensors, and are quite different. Looking at the wiring diagram, these 2 A/F sensors share the +B (12V plus, yellow wire) hot connection, then the yellow wire goes the the A/F relay. So I would suspect something with that relay, or the connections to it.
Thank you for the clarification and excellent diagrams. I assumed A/F was Lexus/Toyota speak for O2 sensor. Will check the relay and connections.
The grounds for the A/F relay are shared with the EFI relay, so if the car is running, they are likely ok. The hot to trigger the A/F relay violet wire, does indeed end up at a fuse as suggested above:
Thanks - I checked all three fuses and they appear to be fine. Is there any reason to swap them out anyway?
I would be tempted to measure voltage to ground on the yellow wire to the bank 2 A/F sensor, it is easy to get to, maybe check the ground (blue wire) while you're there.
A quick update - I left the battery on the charger/maintainer for about 7 hours and then spent the afternoon re-checking fuses and reviewing every wire connection. I replaced the wire nuts used on the black, red, yellow and blue wires. I also tidied up some of the routings used for various wires. I happened to have a volt meter that plugs into the cigarette lighter and as was suggested, I checked the voltage throughout the afternoon (it ranged from 12.2 sitting and 13.3 running). I have reinstalled the stereo and we drove the car for about 90 minutes this evening. So far, no codes or errors. I am cautiously optimistic that perhaps it was indeed a battery drain or wiring issue. I spoke with the installer who indicated they did not pull any fuses or disconnect the battery. He was very agreeable to look at everything which I will do if the codes return. I will update the thread should things change. Thank you to all for the great suggestions.
A quick update - I left the battery on the charger/maintainer for about 7 hours and then spent the afternoon re-checking fuses and reviewing every wire connection. I replaced the wire nuts used on the black, red, yellow and blue wires. I also tidied up some of the routings used for various wires. I happened to have a volt meter that plugs into the cigarette lighter and as was suggested, I checked the voltage throughout the afternoon (it ranged from 12.2 sitting and 13.3 running). I have reinstalled the stereo and we drove the car for about 90 minutes this evening. So far, no codes or errors. I am cautiously optimistic that perhaps it was indeed a battery drain or wiring issue. I spoke with the installer who indicated they did not pull any fuses or disconnect the battery. He was very agreeable to look at everything which I will do if the codes return. I will update the thread should things change. Thank you to all for the great suggestions.
If a shop used wire nuts on my install I'd never go back, they have no place in automotive usage always either butt connectors or solder/heat shrink. Wire nuts are a hack job I'd be very suspect of the rest of their work. I replaced my head unit a year no wire nuts. Again barring sme really rare thing like them cutting a wire to the TCM I think you'll find it will right itself after a few miles or relearning once your battery gets back to proper voltage and the TCM/ECM relearn and play nice together. Wire nuts belong in construction not in automotive use.
08-14-24, 08:56 PM
P0031 and P0051 Codes - Coincidence???
