2000 Toyota Sienna 6 cyl Two Wheel Drive Automatic 204000 miles
Started receiving these three codes in June. Replaced MAF/IAT sensor (IAT is part of the MAF on 98-03 Toyota Sienna), and all three codes disappeared for about 4 months. With colder weather, engine is running more loud and rough when started and codes are back. Codes appear to clear themselves on longer trips and maybe warmer weather.
Checked MAF sensor resistance (terminals 4 & 5) and resistance is within 2.2 -2.7 K ohm range at 68F. Sensor inside looks clean. MAF connector (terminal 4) has 11.8V, so everything appears to be OK. Could ground be open near MAF sensor?
Removed O2 sensor (bank 1) and it looks normal (small amount of gray carbon deposits on a louvered steel cylinder that protects sensor). Didn't tested yet. Both O2 and air sensors (before and after cat) were replaced in 2008.
I am open to your suggestions. I do not have OBD II scan tool and read codes at AutoZone. Thanks.
When more than 1 code appears for a cluster of sensors, the usual cause is a bad connection. Did you check/cleans the connector terminals? At times the terminals are contaminated and over time they would intermittently fail.
Check the wire harness for internally broken parts which would intermittently cause the CEL to show. Wiggling or gently tugging at the wires would make some difference.
It is possible for the ground wire to be the cause but it is shared by a few other sensors and the Transmission Control Module and those would be affected if it is the case. The only possibility is that the wire is broken internally near the MAF, which can occur due to long term vibrations.