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Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
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CEL on p0125 1998 3.0L sienna, seems to run well. Had 02

Customer Question

CEL on p0125 1998 3.0L sienna, seems to run well. Had 02 sensors(2) replaced, also have new thermostat and coolant senor replaced. New battery as well. Toyota dealer says I need a new engine
Submitted: 1 year ago.
Category: Toyota
Expert:  Toyota Service replied 1 year ago.

Hello. Welcome to Just Answer. Please allow me to assist you. You have a p0125 and they are telling you to replace the engine??????

Customer: replied 1 year ago.
Hence the question to you. Have had CEL light continue after two upstream 02 senors replaced, also told thermostat and ducoolant sensor need replacing. All done, CEL still on. In the past 13 months have new battery, radiator and cap and last year got new Cat converter due to leak. Toyota dealer, (after thermostats and coolant sensor) says the light is still on ecause I either need a new engine, or head gasket. He looked with Boroscope and saw deposits on valves. Thought he smelled coolant.
Expert:  Toyota Service replied 1 year ago.

Hello. A P0125 indicates "coolant temperature insufficient for closed loop operation". That means that either the thermostat is faulty, the cooling fans run all of the time, or the coolant temperature sensor is faulty. If the engine is not consuming oil, rapping or making other weird noises, and is not consuming coolant, you should not need a motor. If there is not a genuine 192 degree Toyota thermostat in this vehicle, you need to get one installed. Regarding deposits, I would expect this to be so. All valves have deposits on them over time and miles. Bore scopes are over-rated. They tell you noting about a P0125 code, and, if your guy is using a borescope to diagnose a P0125, he is not doing the diagnosis properly

Customer: replied 1 year ago.
The Koons Tyson Toyota dealership, installed the new thermostat and coolant sensor valve this week ( I assume the parts are Toyota, they cost enough). CEL still on. In my research (online of course...may not be all true) the p0125 in a Toyota of this vintage may be fuel mixture related. The tech Vladimir, said there is a 5% random misfire which is not bad. He inspected plugs and coils which are OK, used the scope and thought he smelled some coolant in cylinder 1. Told me I need a head gasket or a new engine. They replaced the thermostat, coolant sensor, charged 800.00 and the light is still on.
Expert:  Toyota Service replied 1 year ago.

Koons Tyson is a very good service department, but, the P0125 is coolant temperature. He needs to look at the scan tool real time dat values and see what the actual coolant temperature is. If it is not above at least 182 degrees F, the new thermostat is faulty. A head gasket issue would set a P0301 (assuming cyl #1 had a head gasket leak). Not a P0125

Expert:  Toyota Service replied 1 year ago.

It is also possible that the air/fuel mixture sensors are contributing to this issue. These are the first sensors after the exhaust manifolds. If they have not been replaced, I would replace both.

Expert:  Toyota Service replied 1 year ago.

Before you do anything else, get a can of really good fuel injection cleaner (we use a product called BG 44-K). Add a can and drive the vehicle; run the gas out as fast as you can as the product loses strength if it sits). The product will clean the injectors, clean the sensors and might be all that you need.

Expert:  Toyota Service replied 1 year ago.

it will also clean off the 'deposits'.

Customer: replied 1 year ago.
I have read about tests one can do to check integrity of head gasket, shouldn't a tech have done this before making a diagnosis. I will certainly try the injector cleaner first as well. Will the light go off if things are cleaned out?
Expert:  Toyota Service replied 1 year ago.

If the injectors or the sensors are the issue, one or two cans should do it, but the light will not go out instantly. It may need to be cleared. There are tests for head gasket integrity, and are rather easy to do on the side of the engine facing the radiator. If he is telling you you have a head gasket issue, he needs to back it up with a valid test. The last thing you want is to pull the heads and still have the problem.

Customer: replied 1 year ago.
I will call him back to get some answers for you. Naturally, I was a bit taken aback and flustered when he told me all this. I did manage to get the Asst Service Manager to get me to talk to the tech face to face. Can you give me about 30 min to see if I can get him on the phone again?
Expert:  Toyota Service replied 1 year ago.

sure......... if it runs OK, the issue is not severe. A head gasket issue would cause a misfire and you would notice that driving and idling

Customer: replied 1 year ago.
I am waiting for a call back. The issue is severe enough to keep the CEL light on, and my car will not pass inspection.
Expert:  Toyota Service replied 1 year ago.

When I meant severe, I meant expensive engine tear down.