B0004 - PCM Discrete Input Speed Signal Not Present

B0004 is a code that tells you there is something wrong with how fast your car is going. The computer in your car (PCM) needs to know how fast your car is going to control the engine and the transmission.

It gets this information from sensors that measure the speed of your car and the speed of the transmission.

Sometimes, the PCM does not get this information because of a problem with the sensors or the wires that connect them. This can cause B0004. This code can be because of:

• A bad sensor that measures the speed of your car (VSS) or the speed of the transmission (ISS) 
• A bad wire or connector that connects the sensor to the PCM
• A bad PCM

Some signs that you have B0004 are:

• Your check engine light is on
• Your speedometer does not work
• Your anti-lock brakes do not work
• Your transmission shifts badly
• Your engine stalls

To fix B0004, you need to do these steps:

• Check the sensor that measures the speed of your car (VSS). This sensor is usually located on the transmission or the differential. You can use a scan tool to test if it is working properly. If it is not, you need to replace it.
• Check the sensor that measures the speed of the transmission (ISS). This sensor is usually located on the transmission input shaft. You can use a scan tool to test if it is working properly. If it is not, you need to replace it.
• Check the wire or connector that connects the VSS or ISS to the PCM. You can use a multimeter to check if there is any damage or corrosion. If there is, you need to fix or replace it.
• Check the PCM for any damage or corrosion. The PCM is the main computer that controls your engine and transmission. It is usually located under the hood or under the dashboard. You can use a scan tool to test if it is working properly. If it is not, you need to replace it.

The cost to fix B0004 depends on what is causing it. If the VSS or ISS is bad, it may cost around $100-$200 to replace it. If there is a problem with the wire or connector, it may cost around $50-$100 to fix it. If the PCM is bad, it may cost around $500-$1000 to replace it.

You cannot prevent B0004, but you can help your VSS and ISS last longer by keeping your engine oil clean and at the right level.

B0004 is a code that means there is a problem with how fast your car is going. This can cause your car to run badly and use more gas. If you have this code, you should have your car checked by a mechanic.