P0118 with New Sensor, New ECM, and Good Harness, No Voltage

BLUF: New coolant sensor, new ECM, harness resistance and insulation resistance are all good. No voltage at the plug to the coolant sensor on the head.

The lady's Prius had a run-in with a stick at highway speed that went through the radiator. The resulting loss of coolant and overheating blew the head gasket. As I learned from the forums, it was about time for it anyway since it was just over 100k miles.

Thanks to the heroes here on PriusChat, I've replaced the head gasket, water pump, thermostat housing, timing chain, and timing chain tensioner. Due to the amount of coolant that ended up in the oil, I replaced the bottom end bearings and upgraded to the newer style piston head and rings while I was at it. The radiator, AC condenser, fans, and spark plugs were replaced by a shop. I replaced the throttle body after a P0123 code.

P0118 is the last code I have to clear. There's no voltage at the plug to the coolant temperature sensor on the head. The resistance of the harness is less than one ohm. The sensor is new. I checked the resistance of the sensor from D28-64 and 65 and it's 1.4 - 1.5 kohms, right in the band for my ambient temperature and identical to the EGR coolant sensor. I checked the harness to ground per the troubleshooting guide and it's over 50 mohms. There's no voltage at the plug with the car on. I checked the EGR coolant sensor at the same time and it has 5 volts. When I use Car Scanner I get a normal temperature on the EGR coolant sensor and -40F on the head sensor. So I replaced the ECM. I still have the P0118 code and the guide ends there.

Am I missing something?

 

I backprobed D28-64 and 65 and there's no voltage there. I don't have an internal diagram of the ECM to see where that 5V supply comes from. I feel like there should be other sensors running on a 5V supply so I should have more codes if there were a common 5V supply that was bad. The car did run for a few seconds before a fluttering oil control solenoid killed it. So that tells me the rest of the ECM is getting power. Not sure if the oil control solenoid issue is related to the coolant temperature issue since the coolant temperature is an input to the VVT circuit. One thing at a time :sweat_smile:

 

I snuck a couple strands of wire under the connector and found 5V. The connector holes have been rounded open like someone used fluke leads that were too big for the hole. Now to figure out how to get this connector apart. I just watched Haltech Dave's video on depinning connectors and Tyco is featured, but he depinned a little guy, not this monstrosity.

 

So it turned out that the connector receptacles were bent open just slightly enough to not make contact. I pulled the cover off and then squeezed them in both directions with some baby needle nose pliers. Problem fixed.

I started it up, it ran smooth for a couple minutes, then made a high pitched whine. I have codes P0340 and P0343. This thing never ends..