OBD-II Code P1604 — What It Means & How to Fix It

What Does This Error Mean?

P1604 is a startability malfunction code, most commonly seen on Toyota and Lexus vehicles. It means the PCM detected a problem during the engine start sequence. This could be related to the starter signal circuit, crank signal, or an internal PCM fault. Some vehicles will set P1604 any time the battery is disconnected or goes dead. It often appears alongside other codes that point to the real underlying fault.

Affected Models

Very common in Toyota Camry, Corolla, and RAV4
Common in Toyota Tacoma and Tundra
Common in Lexus RX and GX series
Seen on some Scion models sharing Toyota platforms

Common Causes

Battery discharged or disconnected, causing PCM memory reset
Weak or failing battery that causes abnormal voltage during cranking
Faulty starter relay or starter circuit problem
Crankshaft position sensor fault preventing proper crank signal during start
Internal PCM fault — software error or hardware failure

How to Fix It

Check and test the battery. Load test it or have it tested free at an auto parts store.

A battery that drops too low during cranking is the most common cause of P1604 on Toyota vehicles.
Inspect battery terminals and all ground connections. Clean corrosion and ensure tight connections.

Poor grounds can cause erratic voltage swings that trigger PCM errors during startup.
Check for other stored codes alongside P1604. Address those codes first.

P1604 is often a secondary code triggered by a deeper fault such as a crank sensor or ignition issue.
Clear the code and attempt to start the vehicle several times under normal conditions.

If the battery was recently replaced or disconnected, P1604 may clear itself after normal drive cycles.
If the code persists with no other codes present, have the PCM inspected or tested by a dealer.

Toyota dealers have specific diagnostic routines for P1604 and can verify PCM integrity.

When to Call a Professional

P1604 diagnosis starts at $75 to $100 at most shops. If only a battery replacement is needed, cost is $100 to $200. Starter relay replacement is $20 to $60. PCM replacement is $200 to $800 depending on the model.

Frequently Asked Questions

My Toyota shows P1604 after a new battery — is that normal?

Yes, this is very common on Toyota vehicles. Disconnecting the battery resets the PCM memory and can trigger P1604. Clear the code and drive normally for a few days. The PCM will relearn and the code should not return if everything is functioning correctly.

Can P1604 cause a no-start condition?

P1604 itself is a symptom code, not typically the root cause of a no-start. However, if it is paired with a crank sensor fault or severe battery failure, the car may not start. Address all stored codes before concluding that P1604 is the primary problem.

Is P1604 a serious code?

It can be serious depending on the cause. If it is only triggered by a battery disconnect, it is minor and will self-resolve. If it keeps returning with no obvious battery or power issue, the PCM may be failing — that is a serious and expensive repair.