P1604 Code Toyota – Startability Malfunction (Explained)

Do you have problems starting the engine, engine stalling, or misfiring? These are the common symptoms of the P1604 Toyota code.

It can be frustrating when your car cranks but the engine fails to start, especially if you are late for work. You, therefore, need to resolve the code P1604 before it is too late. P1604 is a diagnostic trouble code that shows a problem with the engine.

What causes the P1604 code in your Toyota, and how do you fix it? Read on for detailed information, including how to diagnose this code.

What Does P1604 Toyota Code Mean?

P1604 Toyota code is set if there is a startability malfunction. It is set if the car cranks but the engine does not start after a specified time. But what can make your engine not start? The obvious answer is an empty tank, but there are more reasons.

P1604 Code Toyota

Starting an internal combustion engine involves a chain of events. The starting system, glow system, fuel system, and compression components should all function properly for a successful engine start. Any fault results in an engine startability malfunction.

Symptoms of P1604 Toyota Code

Apart from the engine not starting, the P1604 code also has many other symptoms. They may vary from one model to another, but the most common ones include the following:

  • Hard starting
  • Check engine light on
  • Engine stalling or misfiring
  • Decreased engine performance
  • Car not starting at all

Related content: P1133 Code Toyota – HO2S Insufficient Switching Bank 1 Sensor 1

Causes of Toyota P1604 Diagnostic Trouble Code

Some causes of the P1606 Toyota code are straightforward to diagnose. But some are embedded deep in the systems and require professional diagnosis. In general, they include the following:

Low Battery Charge

The first suspect for the P1604 code should be the battery if the car does not crank. Your car’s battery provides electrical power to the starter motor. The motor does not get enough electrical energy to crank an internal combustion engine. Bad connections or corroded terminals are also possible culprits.

The battery may be dead, or the problem comes from the charging system. If the alternator fails, it no longer charges the car’s battery as it should. So, there will be a lack of power for cranking the engine.

Defective Starting System

A car starting system consists of the battery, ignition switch, neutral safety switch, starter relay, starter motor, and connecting wires. A problem with one or more of these will affect the system, resulting in failed engine start. Your car starting system may be the culprit. But you can eliminate the battery, ignition switch, and starter motor if the car cranks.

Low-Quality Fuel

Low-quality fuel clogs injectors and destroys spark plugs. With these vital engine components failing, getting the engine to start takes more and more time. Eventually, you will have to replace them to get the engine to start. Use the best quality fuel you can find to avoid code P1604.  

Clogged Fuel filter

The fuel filter catches impurities in the fuel that flows to the engine. Over time, it becomes clogged. That reduces the fuel pressure, which reduces the amount of gasoline delivered to the combustion chamber to start the engine.  

Faulty Fuel System

An internal combustion engine requires the right amount of fuel pressure to start. The fuel system should provide it. But if it is faulty, it fails to perform.

A faulty fuel system is due to a clogged fuel line, lack of fuel, frozen fuel, air bubbles, defective fuel pump, injector assembly, or the common rail assembly. You should diagnose the system and fix any problem.

Related content: C1241 Code Toyota – Low Battery Positive Voltage (Explained)

Faulty Engine Control Module (ECM)

ECM should be the last possible cause of the P1604 Toyota code to come to mind. This module monitors sensors in the engine bay and manages the air-fuel mixture for optimal performance. If faulty, the air-fuel ratio can be too lean or rich, and the firing may not be appropriate. But all these should be precisely controlled for an engine to start.

Engine Problem

The engine may fail to start if it is a faulty component. Some common problems include high temperature, too high engine friction, insufficient compression, and faulty engine temperature sensor. Check your coolant and engine oil. Also, diagnose the sensor and replace it if it has an issue.

How to Diagnose

Diagnosing the P16034 Toyota code is the same as finding the specific cause and fixing the problem. The first suspects are the battery, fuel system, faulty starting system, low fuel quality, and blocked fuel filter.

Before further diagnosis, ensure you didn’t have an empty fuel tank when the code P1604 first illuminated the check engine light. Low fuel is one of the most common possible triggers.

The next step is to check your battery voltage, terminals, and connections. If your car is not cranking, it could be a low battery voltage or disconnection in the wiring. Measure the actual battery voltage and clean all corrosions. Replace a damaged ground strap and other connections to the battery terminal.

Check your fuel system for any faults. Unblock a clogged filter and ensure the fuel pump is working. You can even measure the fuel pressure if you have the gauge. Inspect the entire system for any possible cause of failure.

Check the starting system. Is the starter motor functioning as it should? Check if it receives the correct voltage and can crank the engine. Inspect ignition and neutral safety switches, including all wirings in the system.

Next, check the coolant and engine oil to ensure you have the right amount and type. Also, check the engine temperature sensor for any defects if necessary.  

Reset the P1604 code and start the engine. If it appears again, check the ECM. It rarely fails but can also be the possible cause of this error code. It should be the last item to inspect.

Related content: P1683 Code – Meaning, Causes, and Solution

How to Fix P1604 Code

You should fix the P1604 Toyota code as soon as possible. The process involves diagnosing your car for a specific cause and taking the appropriate action. The following are some of the common fixes to consider:

  • Cleaning or replacing the clogged fuel filter
  • Replacing damaged batteries or ground straps or cleaning corroded terminals
  • Repairing the starter motor or replacing it if damaged.
  • Changing engine oil, topping up coolant, or replacing engine temperature sensor.
  • Removing air bubbles from the fuel
  • Replacing ECM
  • Replacing spark plugs and ignition coils


P1604 Toyota code shows that there is an engine starting problem. It is set by PCM when the engine takes long or fails to start after receiving the start signal. The most common symptoms include a hard start, illuminated check engine light, and engine failing to start. Causes are many and vary from model to model. Regardless, you should diagnose and fix it as soon as possible.