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Failed a SMOG test


I am the owner of a Toyota Camry LE 2000 and its been running great but for some minor issues which are addressed from time to time. The mileage is about 140K. I have never failed a SMOG Test and this is the 1st time, I was asked to go to a SMOG Test Only Center. I failed the SMOG Test for the first time. The Functional Check shows FAIL. The OBD Fault Code is “PO128 Coolant Temperature Below Thermostat Rating” and “P1780 Manufacturer specific code”. Does anyone know what this means and what it takes to fix the issue?. I also get a “check engine light” and in general the display is misleading (R will show up when I am driving). My mechanic confirmed its a sensor issue and has nothing to do with the engine.

Now I do have a regular mechanic who works at a SMOG check place (not a SMOG Test place) and he is a very honest person but I am not sure if he is authorized to do this repair and so I am looking for some recommendations. I hate to go to a dealer as you never know what they will charge even if we go for a simple oil change. I am in San Jose, CA. TIA for your time and help.


This is what I got for P1780 and P0128

Can someone please confirm? Thanks

I don’t live in CA, but your post indicates the car was not running at the optimal temperature, meaning the thermostat might need to be changed out for a higher temp thermostat or a new thermostat of the same temp. If the thermostat is stuck open that will affect emissions since the car needs to run at a high temperature to run “clean”.

I’d get a new thermostat and drive the car enough to make sure it up to normal operating temperature when taking it for SMOG testing.

From another forum:

"Code P1780 was a pre-2003 diagnostic code. It wasn’t just an indicator of P/N position switch malfunction. It could also mean a gear position range malfunction or fault. In other words, it might mean there’s no reliable indication of any gear position, not just Park and Neutral.

The P/N switch is involved in ‘signalling’ all the gear positions, but the wires involved for this general purpose are not the same set of wires used in the connections where the P/N switch affects the starter circuit"

P1780 has NOTHING to do with emissions, but they will take the opportunity to flunk you for it anyway…

I am a Ca. Gold Shield C.A.P. Test only and Test and repair in L.A. Your codes though they may not seem emissions related to you if they turn on the check engine light they will cause the the car to fail an emissions test as the OBDII comunication with the smog machine will report the code. P0128 is probably a thermostat not closed or missing and should be replaced with an original equipment part. The trans range sensor will have to be diagnosed. You should check to see if you meet the eligability for the Consumer Assistance Program (C.A.P.) the state provides up to $500.00 toward emissions related repairs however the program is suspended until July 1.

Thanks, Uncle Turbo for your advice on getting a new thermostat. My mechanic wants me to ride 60-70 miles before we can confirm the same. I just have to plan a trip.

Caddyman is right on the P1780. On hindsight, I should have fixed it before going to the test.

I will go with the advice of Pumpkinkrasher but any idea on how much it will cost to replace it?.

Again, thank you all for responding to my post. Appreciate your time.


Did you drive on the freeway for at least a half hour before going for your smog test? The car has to be completely warmed up. That’s what is recommended in MD, and our emissions standards are the same as yours.

I recommend a thermostat change (generally along with a coolant change) every 5 years on a daily driven car.
So if this thermostat is 12 years old I would change it anyway, no need to confirm. Change the radiator cap too.

Thanks Jtsanders and Circuitsmith for taking time to answer my posts. Yes, I should have driven an hour before taking the SMOG test. Anyway. I no longer get the P0128 error anymore but the P1780 keeps coming. My mechanic replaced the electronic piece (in the hood) that gets the signal. It made no difference as I started getting “check engine light” while driving. Other weird indications are coming too but my car drives fine. He is going to replace “gear shift”. He could not get this part easily. Any recos?. TIA for your time.