2009 Sienna shows MIL but no code; how can I diagnose that?

detective99

My 2009 Sienna has turned on the Malfunction Indicator Light but my OBD-II scanner shows "no codes". How can that be? How can I diagnose the problem?

thecardoc3

The instrument cluster can command the light on if it's communication with the PCM is disrupted, or it could happen if the cluster itself has lost the ability to correctly control the lamp. Scan tool bi-directional controls can be used to command the cluster to turn the light on and off and see if it is capable of controlling it.

detective99

Thanks, thecardoc3. I had already used the scan tool to attempt to turn off the malfunction light, but it did not turn off. I live in California where the car must pass a periodic smog test, and they usually won't run the test if the light is on, but if they see that there is no error code, perhaps they will accept the car for testing. Meanwhile, though, do you have any ideas on how to further diagnose and/or fix the problem?

thecardoc3

Do you mean that you tried to clear codes to see if the light would go out, or did you have a full function scan tool and try to command the light off under the instrument cluster and/or PCM menus? If you tried to use bi-directional controls and the lamp won't go out then there are two possible directions depending on how your car controls the light. It's either going to be hard wired to the PCM, which means you will have to test and prove that the wire isn't grounded and if the PCM is falsely commanding it on. Or, it could be controlled by the instrument cluster itself via the communication data bus. If that is the case then the driver for the lamp has failed and the cluster will need to be repaired.

detective99

My scan tool is the OTC 3108N, so it is not a full-function scan tool. I performed the procedure to erase all codes, even though no error code was found. Both before and after the erase procedure the scan tool says that MIL is off, even though the light is on. My scan tool does not provide a way to command MIL to be off or on. So, I guess there is either a problem in the wiring or in the lamp driver