P0000 Code: No Fault Code Stored or Empty Scan Tool Reading

What the P0000 code means

The SAE standard does not define any fault with the number 0000. When it shows up on a screen it almost always means one of two things, and telling them apart is the whole diagnosis.

The first is that there are no codes stored. Many scan tools, especially cheap ones and phone apps, show P0000 as a way of saying the memory is empty. That is a normal result and needs no action.

The second is that the scan tool did not get an answer from the vehicle. It may not be communicating with the module, the protocol may not be supported, or the module you asked may not be the one that stores the fault. In that case the P0000 code says nothing about the engine. It says the read failed.

There is a third scenario worth keeping in mind. If the check engine light is on and the scanner insists there are no codes, the fault is most likely in a module other than the engine computer, such as the transmission, ABS or body control, and your tool is only reading the emissions module.

One more situation confuses a lot of people: permanent codes. On modern OBD2 vehicles there are codes that cannot be erased with a scan tool and only go away when the computer itself confirms over several drive cycles that the fault does not come back. Some basic tools cannot read them and show a memory that looks empty.

If the vehicle failed an inspection but your scanner finds nothing, ask about permanent codes. They live in a different memory than the usual one and need a tool that knows how to request them.

P0000 code symptoms

• The scan tool shows no code even though the check engine light is on.
• The read is interrupted or never finishes.
• The engine runs normally.
• Other modules do show codes when you query them separately.
• The tool shows this value every time, on any vehicle.
• The vehicle failed an emissions inspection even though the scanner shows no codes.

Likely causes of the P0000 code

1. No codes are stored. This is the most common case and needs no action.
2. The scan tool is not communicating with the module because of a protocol mismatch.
3. The fault is in another module that the tool is not reading: transmission, ABS, airbag or body control.
4. A cheap scan tool with limited firmware that shows this value as its default result.
5. The diagnostic connector has no power because of a blown fuse.
6. Damaged or dirty pins in the diagnostic connector.
7. A weak battery, which prevents stable communication.
8. Codes that were just cleared, so the memory is still empty.
9. Permanent codes stored in a memory that basic tools do not query.

How to diagnose the P0000 code step by step

1. Check whether the check engine light is on. If it is off and the scan tool shows no codes, everything is fine and there is nothing to repair.
2. If the light is on, read all modules, not just the engine. The fault may be in the transmission, ABS or body control, and a basic code reader cannot reach them.
3. Confirm the scan tool is really communicating by pulling up some live data, such as engine rpm. If it cannot show that either, the problem is communication.
4. Check the fuse for the diagnostic connector. On many vehicles it shares a circuit with the cigarette lighter.
5. Inspect the connector pins for dirt, corrosion or pushed-in terminals.
6. Try another scan tool, preferably one that covers all modules.
7. Test the battery. Low voltage prevents stable communication.
8. Ask about permanent codes if the vehicle failed an inspection and your scanner finds nothing. They are stored in a different memory.

How to fix the P0000 code

• If the check engine light is off, do nothing. There is no fault to repair.
• Use a scan tool that reaches all modules if the light is on and the engine module shows no codes. A P0000 code in that situation tells you to look elsewhere, not that the car is fine.
• Replace the diagnostic connector fuse if no power reaches the connector.
• Clean the connector pins with electrical contact cleaner.
• Replace or recharge the battery if its voltage is too low to communicate.
• Try a different tool before you assume the vehicle has a communication problem.
• Use a tool that can request the permanent code memory. Those codes cannot be erased with a scanner and only go away after several drive cycles without the fault.

Technical reference data

• The SAE standard does not define any fault with the number 0000.
• The diagnostic connector gets constant power on pin 16 and ground on pins 4 and 5.
• On many vehicles the connector fuse is shared with the cigarette lighter.
• A basic code reader only reaches the emissions module. Transmission, ABS and body control need extended coverage.
• Minimum voltage for stable communication: above 11 volts.
• Permanent codes are kept in a separate memory and cannot be erased with a scan tool.

Brand-specific notes

Before you decide the vehicle is faulty, check whether your scan tool can read live data. If it shows rpm and coolant temperature, communication works and the memory is simply empty. If it shows nothing, the problem is the tool or the connector.

The most common case in shops is the third one: check engine light on, a basic reader that finds nothing, and the real fault sitting in the transmission or ABS module. A scan tool with full coverage settles it in a minute.

Frequently asked questions about P0000