I recently replaced the starter on my SC400 and after a long day of work the car started again but was throwing a check engine light and overheating. I ran diagnostics and got a code 31 which is for the mass airflow sensor. The sensor was clean and everything so i immediately assumed it was a bad connection somewhere.

Long story short the car kept overheating so I took it to a shop and they said it needed a water pump because they ran it without a thermostat and it still overheated. I told them i was going to get a second opinion because i felt it was too much of a coincidence for the water pump to fail exactly while i was replacing the starter.

*** After using an ohmmeter and service manual my dad and I found the overheating was due to the check engine light. There is a bolt on the rear right cylinder head that i forgot to replace that is a ground for the mass airflow sensor and engine. I circled the two rear grounds on the photo and the one in red is the one i forgot to replace. Make sure you remember to replace these two bolts!