treeman

Hello there everyone, I am new to this and have been reviewing old post for some time. I have a 94 ls400, the heat will not work. I have changed tstat, purged system, ran diagnostics, check fluid levels and I am still cold. If anyone can help, please do...thanks me the tree

Amskeptic

If coolant level is good, go to the firewall and look for a heater hose leading to a valve. With heater on and engine warm, see if the hose is warm on both sides, or just one side, or not at all.
Both sides says the heater valve is open and your problem has to do with airflow.
One side says valve may not be opening.
Both sides cold says you have an obstruction, or air lock.

A mechanical failure of the valve will not show up in the diagnostics. On my '92, the cable was not shutting off the valve fully, so I had too much heat . . . in the summer. I re-connected the outer cable clamp with the valve firmly shut, and no problemo.
Colin