Toyota does not provide primary or secondary resistance specifications for the ignition coil units used on these models, making it necessary to substitute a known good unit for testing, which is not practical for home mechanics due to the inability to return electrical components once purchased. If all other potential causes of ignition malfunction have been ruled out, a defective ignition coil or igniter unit is likely the issue, and verification requires substitution with a known good unit. For a suspected coil, visually inspect it for cracks using a magnifying glass and check its resistance with an ohmmeter to see if it significantly differs from the others. Begin by disconnecting the cable from the negative terminal of the auxiliary 12-volt battery, ensuring to perform the Initialization procedure upon reconnection. For models from 2001 to 2003, remove the air cleaner assembly; for 2004 to 2009 models, take out the interfering engine compartment relay block; and for 2010 and later models, remove the windshield wiper motor and linkage along with the cowl assembly. Next, disconnect the electrical connector(s) from the coil(s) and remove the mounting bolt(s), as the four ignition coils are accessible on top of the valve cover, each secured by a single bolt. Carefully withdraw each coil from the cylinder head, and installation follows the reverse order of removal.