This one is interesting...car (not mine but customers) was throwing a code saying communication between throttle pedal and ECU malfunction. Literally no movement other than idling forward or reverse. Throttle pedal was replaced, throttle BODY was replaced....Dealership says damage to "harness" caused by heat or rodent chewing and that harness should be replaced. We did find high voltage harness (far right connector on Inverter) downstream to be slightly melted mid harness from something, Check Hybrid System with triangle on dash with several other non related codes present. Without specific codes, going in blind..what would you diagnose first? Something glaringly obvious or anyone have the same no-communication between throttle pedal and ECU before? Dealer stumped, customer stumped..head scratching and don't want to rabbit hole every little possibility.
^ this: please post the actual code(s). It's important because the fortune cookies, which are never very helpful in general, are super unhelpful for these codes, because the sensor on the pedal and the sensor on the actual throttle both need trouble codes, and Toyota chose to use codes in the SAE standard P0 and P2 ranges that all have fortune cookies like "Throttle / Pedal Position Sensor" regardless of which sensor they mean. Details are in this post. Between both those sensors and the ECUs, what happens is only "communication" of the most rudimentary kind: the sensors just make voltages that change with the position. Also, they "communicate" with different ECUs: the throttle sensor is wired to the ECM, but the pedal sensor is wired to the power management control ECU.
Code is P2122/38 Throttle/pedal position sensor/switch circuit low and voltage correlation. Throttle pedal data shows no communication in between pedal and computer at accelerator pedal position 1, the pedal was already replaced with a working one. All known wires reading possible communication problem in wire harness assembly.
Two codes, then. P2122's full fortune cookie is Throttle/Pedal Position Sensor/Switch "D" Circuit Low Input, and P2138's is Throttle/Pedal Position Sensor/Switch "D"/"E" Voltage Correlation. The way Toyota piggybacked on the SAE standard codes, they used "A" circuit and "B" circuit for the throttle position, and "D" circuit and "E" circuit for the pedal sensor. So both these codes are definitely about the pedal. "Communication" is an overblown word for what happens from the pedal to the computer; the pedal just puts out voltages. It looks like this: VCP1&2 are just power to the sensor, EP1&2 are grounds, and VPA1 and VPA2 are the pedal position signals that matter. They are nothing but voltages that rise on straight lines from pedal-released to pedal-floored. VPA1 and VPA2 come from two independent Hall sensors inside the pedal that give matching outputs except that VPA2 is about 0.8 volt above VPA1. The ECU can make sure it sees that 0.8-volt-apart match, or it knows something is wrong with one signal or the other, and gives the miscorrelation code. In this case, you also know which signal is probably messed up, given the P2122 code saying it's circuit "D" that just looks suspiciously low. I'm guessing Toyota would have used "D" to mean VPA1 and "E" to mean VPA2. You can read Accel Pedal Pos #1 and Accel Pedal Pos #2 in the Hybrid Control data list (though they are converted there from the expected voltages into 0–100%, and I'm not sure what they'll show when the ECU has already decided it doubts the input). You can also just grab a voltmeter and look. VCP1&2 should be 5 volts, EP1&2 should be ground, and VPA1 and VPA2 should do what you see in the above graph. That's all that's going on here; calling it "communication problem" blows it out of proportion. One of those voltage inputs reaching the ECU isn't right; find out why, and fix it.
Thanks! So..Not ECU itself bad, but wiring harness (damage from rat or melting somewhere) OR Throttle pedal itself (which was changed already, but possibly still bad)? Came in with check hybrid system triangle and message as well..
Well, the A/D converters that measure those voltages are inside the ECU, so if your voltmeter tells you the right voltages are getting as far as the ECU pins and the ECU still says they're wrong, then it could be at fault. Probably more likely you find the problem elsewhere though.
Bringing this back up: Changed out ECU to used unit that works and the car became "mobile" again, as in it drives and moves now. Still throwing P2122 & P2138 with a Check Hybrid System triangle warning after it sits a couple hours. It has a "new" refurbished HV battery in it now but still same codes, sometimes gets stuck in Park. Also has new throttle pedal, nothing..
Use multimeter, diagram, and explanation of circuit, trace source of problem, fix. Even with fancy newfangled stuff, sometimes it's the old-skool skills that do the job.
