2001 Montero with code 403. Should I replace the EGR solenoid, the EGR valve, or both?
You can replace both parts but still have the problem. Do a little diagnosing before you replace parts. It could be as simple as a broken vacuum line.
Make sure you have a vacuum source to the EGR valve. Wait for the engine to warm up and check to see if there is vacuum at the EGR valve, race up the engine to be sure. If there is no vacuum then check the source at the solenoid. If you have vacuum before the solenoid then it is possibly the solenoid.
Apply vacuum to the EGR valve to see if the valve is working. If you apply vacuum and the EGR valve doesn't work then replace the EGR valve?
If the entire EGR system seems to check out then remove the valve and see if there is a carbon blockage in the EGR port.
If you need more information then get back to me and we can diagnose the problem further.