Check engine light - MAF sensor or EGR system

TACOMAOWNER

MEMBER
2001 TOYOTA TACOMA
2.7L
4 CYL
2WD
AUTOMATIC
186,000 MILES

My truck seems to be running fine with no apparent issues but the CEL came on so I took it to both Autozone, then to O'reily for reading codes. Both places showed only one code: P0402. I took it to my Toyota dealer, they had codes P0100, P0110, and P0402. They reset CEL and insisted that if light comes back on then the MAF sensor ($1,100.00) needs replaced. After about 80 miles it came back on. I decided to try cleaning the MAF sensor and reset CEL. Again, it came back on. I have heard that by disconnecting the MAF sensor while the engine is running and the engine shuts off, then the MAF sensor is okay, and does not need replaced. Is this true? I did this and my engine does shuts off immediately after disconnecting MAF sensor. I have also heard that a P0402 code usually means that the EGR valve is stuck open and the dpfe sensor is probably faulty and to test that first. I would hate to replace the expensive MAF sensor, only to find out the problem lies elsewhere. Any suggestions?

3 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good morning.

You cannot clean the mass air flow sensor. The carbon burns on to the sensor and there is no cleaner that can remove burned on carbon. There is also no reset for the sensor as well.

The test disconnecting it is not a valid test at all.

Below is some possibilities for the 402 code that needs to be checked.

Also some possibilities for the mass air flow sensor codes

Roy

The EGR system recirculates exhaust gas, which is controlled to the proper quantity to suit the driving conditions, into the intake air mixture to slow down combustion, reduce the combustion temperature and reduce NOx emissions. The amount of EGR is regulated by the EGR vacuum modulator according to the engine load.

If even one of the following conditions is fulfilled, the VSV is turned ON by a signal from the ECM.

This results in atmospheric air acting on the EGR valve, closing the EGR valve and shutting off the exhaust gas (EGR cut-off).

Under the following conditions, EGR is cut to maintain driveability.
- Before the engine is warmed up.
- During deceleration (throttle valve closed).
- Light engine load (amount of intake air very small).
- Engine racing.

Wiring Diagram
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System Check Driving Pattern
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SYSTEM CHECK DRIVING PATTERN
a. Connect the OBD II scan tool or TOYOTA hand-held tester to the DLC3.
B. Start and warm up the engine with all the accessories switched OFF.
C. Run the vehicle at 70 - 90 km/h (43 - 56 mph) for 3 minutes or more.
D. Idle the engine for about 2 minutes.
E. Do steps (c) and (d) again.
F. Check the READINESS TESTS mode on the OBD II scan tool or TOYOTA hand-held tester.

If COMPL is displayed and the MIL does not light up, the system is normal.
If INCMPL is displayed and the MIL does not light up, run the vehicle step (e) from some times and check it.

HINT: INCMPL is displayed when either condition (1) or (2) exists.

1. The system check is incomplete.
2. There is a malfunction in the system.

If there is a malfunction in the system, the MIL will light up after steps (b) to (e) above are done (2 trip detection logic).

INSPECTION PROCEDURE

HINT: Read freeze frame data using TOYOTA hand-held tester or OBD II scan tool, as freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. At the time of the malfunction.

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