I have an active P2181 with a pending P0128. No change in either status since the Fault light lit.
1. I replaced the thermostat with a new tested one that maintains the prescribed temp (195F).
2. I've replaced the ECT sensor with a new one.
3. I've fully drained (including the block), flushed, refilled, and have run/driven it at NOT (Normal Operating Temperature) for over 40 minutes.
4. The displayed temperature on the dash shows just slightly under the center mark - about where I'd expect for a 195F t-stat. My bluetooth scanner shows that when idling, the temp settles at 195.8F, so, the ECT is sending an acceptable temp to the PCM.
5. After several warmups/cooldowns, the coolant level is still good (just above the cold fill line after the engine has cooled to ambient.

So, I'm at a loss at this point. Any suggestions other than taking it to a shop where they'll probably want to do exactly what I've already done?

 

Have you tried clearing the codes? Not sure if those automagically reset themselves or not.

 

with a smog check due by tomorrow I'm kinda reluctant to clear the codes manually at this time...

 

It won't pass with the codes present either..... but you certainly won't have the monitors complete by the time you test..... Hobsons choice.

 

Just an update as to the fix:
1. The codes wouldn't clear using a scanner, so I found out that some codes can't be simply cleared by a scan tool as long as a qualifying condition remains.
2. As a quick and easy attempt (even though with an expectation that it wouldn't work) I disconnected the battery and shorted the 2 connectors (NOT the battery terminals!) to drain any stored capacitance, and left the battery disconnected for over 30 minutes. No change.
3. Finally, what DID work was disconnecting all 4 connectors from the PCM, then reconnecting them once they were all connected.

It seems that there might have been a marginal connection in a related pin that threw an erroneous "condition" that caused the error codes. I re-ran the fault scan and came up clean. Even after over 100 miles which included several full warm-up/cooldown cycles, no codes - not even pending.

So, before spending hard-earned $$$ of parts or service, just try a (not-so-simple) disconnect/reconnect on related components on the outside chance that connections just need to be reseated.