Toyota Tech Tip: MIL On, Misfire DTCs Set on 1MZ-FE Engines – UnderhoodService

Toyota Tech Tip: MIL On, Misfire DTCs Set on 1MZ-FE Engines

Some vehicles equipped with 1MZ-FE (V6) engines without VVTi may exhibit a rough idle and/or an MIL-on condition with a diagnostic trouble code or codes for misfire caused by an improperly operating ignition coil assembly. Production changes have been implemented to prevent this condition from occurring.

Applicable Vehicles:
– 2001 model year Japan-built Camry vehicles equipped with 1MZ-FE engines (“6).
– 1998-2001 model year North American-built Camry vehicles equipped with 1MZ-FE engines (“6)
– 1998-’99 model year Avalon vehicles.
– 1998-2000 model year Sienna vehicles.
– 1999-2002 model year Solara vehicles equipped with 1MZ-FE engines produced before the production change, effective VIN 2T1CF2#P*2C578710.

Repair Procedure:
1. Confirm if the vehicle is currently misfiring, ­running rough or hesitating.
If YES – Go to Step 2.
If NO – Review Freeze-Frame Data and attempt to operate the vehicle under similar driving conditions. See notes below for information that makes it more likely to duplicate misfire.figure 1

Note: The following activities will turn off misfire detection:
• Changing engine rpm greater than 150 rpm.
• Changing throttle position quickly. See Fig. 1.

Misfire duplication can be duplicated most readily when the engine speed and throttle angle are held nearly constant for at least 2 minutes.

2. Confirm if the misfire is currently occurring on cylinder(s) identified by DTC(s) using the diagnostic tester while the engine is idling. See Fig. 2.Figure 2
Is the cylinder(s) identified by the DTC(s) misfiring?
If YES – Go to Step 3.
If NO – Follow the normal diagnostics for the applicable DTC in the Technical Information System (TIS) in the ­applicable Repair Manual: Diagnostics: SFI: P030 #.

3. Swap the suspect ignition coil(s) from the cylinder that is misfiring to the cylinder that is not misfiring.

4. Using a diagnostic tester, confirm that the misfire is now occurring in the cylinder that has the suspect ignition coil(s). Has the misfire followed the swapped ­ignition coil(s)?
If YES – Replace the ignition coil(s) and go to Step 5.
If NO – Follow the normal diagnostics in TIS for the applicable Repair Manual: Diagnostics: SFI: P030 #.

5. Confirm that the misfire has been eliminated (0% at all times) using the diagnostic tester while the engine is idling.
Note: If the misfire percent is any value other than 0% at any time, then that cylinder is misfiring.

Technical service bulletin courtesy of Mitchell 1.

For more information on Mitchell 1 products and services, automotive professionals can log onto the company’s website at


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