P0031 and P0051 and 4wd comes on by itself on startup
I could really use some help diagnosing some electrical gremlins I've been battling for a few months now. Happy to try anything you think of before taking it to a professional auto electrician.
Showing P0031 and P0051 codes, always simultaneously. At first they were intermittent, and now show up right away on reset and remain on. OBDII shows no short term fuel trim % or long term fuel trim % on either side, but does show voltage, lambda's and other measurements seemingly in range.
4WD also seems to be coming on by itself either while it's "off" or when I start it up. Selector knob is usually turned as well. Verified I'm not crazy and it's happening by itself periodically.
Background and electrical work done well before codes:
- Battery from 2020 and original alternator and battery cables.
- Upgraded to LED lights all around, including headlights.
- Supercharged including upgraded fuel pump, injectors, spark plugs, cam sprockets, piggyback ECU.
- Switched stereo to the newer GR, replaced speakers and installed Kicker Key 200.4 amp with power straight from battery.
- Added 2x QC3.0 USB charging ports, repurposed the wires directly from the cigarette lighter.
- Added additional LED daytime running lights.
Most recently done prior to codes first appearing intermittently:
- Fuel system cleaning - BG 44k
Immediately before codes appear continuously and quickly after reset:
- While driving, fuel pump tube completely disconnected from circular housing right above the fuel pump, spilling gasoline all over the fuel tank and the road. Little plastic retaining connector seems to have broken, and it may have been loose prior to this failure and been broken for awhile. Replaced and connected and no issues running or starting, but codes haven't disappeared since.
Checked and done so far:
- Fully went through Toyota's service manual checks for fuses, relays, A/F sensors and resistance on wires. Everything seems to have checked out.
- Replaced A/F sensors 3 times. Each time could smell and see them heating up initially, seemingly burning off some coating or such. First were the Denso's, second two pairs were directly from Toyota. Externally verified part numbers with numerous folks.
- Replaced ECU
- Checked voltage at each A/F sensor showing 12.3 volts each.
- Checked the signal wire for continuity from relay.
- Cleaned negative battery terminal and main ground point, as well as the ground point directly below next to the driver's side wheel on the chassis.
- Had Batteries Plus check the battery and they say it's good to go.
I'd hate to give up and take it to a pro at this point, given all the time and money I've thrown at it. My next thoughts were replacing the battery cables with the "Big 7", cleaning connections and grounds, and/or dropping the fuel tank and inspecting electrical and stuff around there.
Any ideas would certainly be appreciated!
