Parts for your 2004 Toyota Mark x-Ignition coils

2004 Toyota Mark X Ignition Coils

Ignition coils are absolutely relevant on the 2004 Toyota Mark X. Technical references including the Toyota Mark X Repair Manual for the GRX120/GRX121 series, Toyota’s Electronic Parts Catalogue, and Denso application data all specify six individual coil-on-plug units for the 4GR-FSE 2.5L and 3GR-FSE 3.0L V6 petrol engines. These GR-FSE “D-4” direct-injection engines run a distributorless, ECU-controlled coil-on-plug system.

On this Mark X, each ignition coil sits directly over a spark plug, stepping up 12 volts to the high voltage needed to fire the mixture. Coil-on-plug improves spark energy, timing accuracy and emissions, and reduces lead losses compared with old-school leads and a distributor. It’s a tidy, reliable setup that suits the GR V6’s smooth, revvy nature.

Ignition coils aren’t a routine replacement item, but they’re worth a look whenever plugs are changed (typically around 100,000 km with iridium plugs). Age, heat and vibration can eventually fatigue a coil or its boot, causing intermittent misfires—often first noticed under load or on cold starts. Typical fault codes include P0300–P0306 (random/cylinder-specific misfires) and P0351–P0356 (coil primary/secondary circuit faults).

• Symptoms: rough idle, hesitation on hills, noticeable flat spots, worse fuel use, and a flashing or steady check-engine light.
• If a code names a cylinder, swapping that coil to another cylinder to see if the fault follows is a quick, reliable test.

Replacement is straightforward and DIY-friendly with basic tools. Stick with quality OEM-spec coils (Toyota/Denso) for consistent performance and longevity. If the car has done big kilometres and one coil dies, many owners choose to replace the bank or full set of six to avoid repeat visits, but it’s fine to replace only the failed unit if the others test well.

1. Confirm the fault with a scan tool, note any P030x or P035x codes.
2. Remove the engine cover, unplug the connector, undo the 10 mm hold-down bolt, and lift the coil. Check the boot for cracking and for oil in the plug tube (cam cover seal issues).
3. Seat the new coil, lightly coat the boot with dielectric silicone, and tighten the bolt to about 8–10 N·m. Reconnect, clear codes and road test.

Preventive care is simple: avoid pressure-washing the engine bay, keep connectors clean and latched, and always run the correct iridium plugs at the proper gap and torque. On the Mark X’s longitudinal V6 layout, both banks are accessible from above, the rear bank is a bit tighter but doesn’t require major disassembly.

Popular questions about 2004 Toyota Mark X ignition coils

How many ignition coils does a 2004 Mark X have, and are they coil-on-plug?
The 2004 Mark X uses six individual coil-on-plug ignition coils—one per cylinder—on both the 4GR-FSE and 3GR-FSE V6 engines. It’s a distributorless system managed by the engine ECU.

What are common symptoms and fault codes of a failing coil?
Expect rough idle, stumble under load, poor economy and a check-engine light. Scan tools typically show P0300–P0306 for misfires or P0351–P0356 for coil circuit faults. Swapping coils between cylinders helps confirm the culprit.

Should coils be replaced individually or as a full set?
Either approach is acceptable. Replacing the failed coil only is cost-effective if the others test fine. On higher‑kilometre cars, many opt to change the full set or at least the affected bank to reduce future downtime.