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


You May Also Like

Cartridge Oil Filters

Mistakes made can result in costly comebacks.

An oil change is probably one of the least expensive services your shop offers, but it can result in one of the most costly comebacks if a mistake is made. Cartridge oil filters make potential mistakes more likely because they require more knowledge and tools to properly change the oil than a canister filter.

Spark Plug Fouling

Understanding why spark plugs get dirty.

Why Alternators Are Subject To Ripple Voltage

The alternator produces an AC current that must be converted into DC current by way of a rectifier.

Understanding Stop/Start Charging and Starting Systems

The problem may not have been caused by a complicated reason, something simple may have caused the system not to work.

Remanufacturing And The EV-Battery Challenge

One researcher is particularly interested in the fate of EV batteries once they reach the end of their automotive lifecycle.

Other Posts

Ford EV Opportunities

Despite what you may imagine, there are still maintenance and repair opportunities in a Ford Mustang Mach-E.

Exhaust Gas Recirculation Operation and Diagnostics

Since exhaust gas does not burn, this lowers the combustion temperatures and reduces NOx emissions from the engine.

CAN Bus Communications

There are three types of bus configurations that you will come in contact with — loop, star and a hybrid of both.

Solving Intermittent Overheating

New cooling systems anticipate and influence changes in coolant temperature.