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Skyvisions, ASE Certified Technician
Category: Toyota
Satisfied Customers: 14412
Experience:  Toyota Master Diagnostic
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fuel system 2 cl fault 0401

Resolved Question:

I cleaned and changed everything I could think of, fault did not come back till I changed air intake temp sensor. Five months later fault returned. I then changed temp sensor in block. Fault did not return for 5,000 miles. Now it comes back two or three times a month. What have I missed? I do not know if this car has a lower O2 sensor, and if it does could it be bad? The car is a 96 Tercel with 176,800 miles.
Submitted: 8 years ago.
Category: Toyota
Expert:  Skyvisions replied 8 years ago.

Do you mean P0401 (insufficient egr gas flow)? Can you give me more details on the sensor that you replaced.



Customer: replied 8 years ago.

Items replaced: upper O2 sensor, engine block temp sensor, IAT sensor, egr valve, vsv, vacuum reg. in egr circuit.


I cleaned the throttle body and all vacuum lines going to it. Cleaned steel pipe on egr valve that runs to exh.


Expert:  Skyvisions replied 8 years ago.

If you apply vacuum to the EGR valve does the engine stumble and stall at idle? Use a hand vacuum pump or a good vacuum source on the engine.



Customer: replied 8 years ago.
The engine will stumble a small amount, but it does not stall.
Expert:  Skyvisions replied 8 years ago.

This is what I suspected. The passage way in the intake manifold is plugged or restricted with carbon. The 4 cylinder Toyota engines will stall immediately when full egr valve function is applied. This will trigger the P0401 restricted flow code.



Customer: replied 8 years ago.
If I unbolt the egr valve from the manifold will the motor run. I assume I can spray carb cleaner into the manifold, but the mass air sensor may prevent the motor from running.Will this become a problem?
Expert:  Skyvisions replied 8 years ago.

This has a MAP system not a MAF system creating a vacuum leak on the egr valve opening will make the rpm race not die or at least until the MAP sensor reaches it limit to increase the fuel injection duration and then it will begin to surge.


My concern would be damage to the converter with the carb cleaner and the chunks of carbon can get stuck on the pistons or valves causing damage. Proceed with caution.


I recommend pulling the throttle body and sticking a rag in under where the pipe bolts onto the intake to catch the chunks. Make sure the egr valve is clean and not plugged on the back of the head.



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