Check Engine light comes on and goes off (PO125 and PO441)

[Volunteer871]

For a few months, I have been getting check engine lights on my Toyota Corolla 2002. The check engine light often goes away by itself.

I took my car to a mechanic with a decent reputation after a couple weeks of the problem. He thought he fixed it and gave the car back to me. The check engine light kept coming back on, and I kept going back. The mechanic topped off the coolant, replaced certain hoses, host clamps, sensors and other parts (like the solenoid canister). After the fifth trip back (and eight weeks of time), he refunded my money.

The check engine light comes on and goes off. Right now with no check engine light on, I get codes P0125 and PO441 PD.

What will happen if I keep ignoring these check engine lights or the codes that persist when the check engine light is not on? I was thinking of going to another mechanic. I think I want to wait for a few more weeks to see if I notice a pattern. I do not drive that many miles each day (much less than average).

[Brian R.]

Here is what I have on these trouble codes:
P0125
Insufficient Coolant Temperature for Closed Loop Fuel Control

Possible Problems
After the engine is warmed up, oxygen sensor output does not indicated RICH even once when conditions warrant and continue for at least 1.5 min.
Conditions: Engine speed 1,500 rpm or more, and speed 25-62 mph and throttle valve not completely closed.

Open or short in HO2 sensor circuit or oxygen sensor

or

Engine coolant temperature (ECT) sensor indicates that the engine has not reached the required temperature level to enter closed-loop operation within a specified amount of time after starting the engine.

Insufficient warm up time
Low engine coolant level
Leaking or stuck open thermostat
Faulty coolant temperature sensor

P0441 and/or P0446
A. Diagnostics for PO441:
1. Remove and replace Vacuum Hoses between EVAP VSV and Charcoal Canister.
2. If there is a metal vapor pipe between EVAP VSV and Charcoal Canister, clean inside of vapor pipe
3. Replace EVAP VSV and Charcoal Canister assembly with new parts.

B. Diagnostics for P0446:

1. Inspect vacuum hoses and pipes between EVAP (Purge) VSV and Charcoal Canister for leaks.
2. Replace Vapor Pressure VSV and Canister.
NOTE :When performing diagnostics for an occurrence of a MIL "ON" condition, Diagnostic Trouble Code (DTC) P0441 may be result of debris in Evaporative Emission Control System. This may cause blockage of a vapor line, or a stuck VSV, as described in troubleshooting area of Repair Manual.

Possible Problems
Open or short in VSV circuit for vapor pressure sensor
VSV for vapor pressure sensor
Open or short in vapor pressure sensor circuit
Vapor pressure sensor
Open or short in VSV circuit for EVAP
VSV for EVAP
Vacuum hose cracks, hole, blocked, damaged or disconnected
Charcoal canister cracks, hole, or damaged

The bottom line of this is: Don't neglect these codes. Bring your car to a competent mechanic. If the engine is not coming up to temperature, then it will never run right. You have to attain closed-loop fuel metering to make the engine perform correctly.