5 Steps to a Successful Diagnosis

I successfully retrieved the DTC (diagnostic trouble code).
Now what?

Movi™ and Movi™ Pro are tremendously helpful tools designed to aid in diagnosis of emissions and driveability malfunctions that may occur in your automobile. Retrieving the DTC is the first step in successfully diagnosing the root of the problem that was detected. Now it's time to decipher this code and move onto the next steps of the troubleshooting process.

There are over 3,000 codes in the OBD2 generic database and several hundred more in manufacture specific codes in the Movi and Movi Pro database. These codes are divided by vehicle system and can be related to several components depending on the problem presented.

Retrieve and identify the code.

The majority of trouble codes displayed while using Movi and Movi Pro will have descriptions following, which will allow the bypass of this step. If a description is not present, the quickest way to find a description is a simple web search of the code.

* Transmission trouble codes may not be supported on all vehicles.
** CAN codes will only be present on vehicles that utilize the CAN protocols.

Vehicle Systems and numbers

P0001-P0299 Fuel and air metering/ Auxiliary
emissions controls/ Injector circuit
P0300-P0399 Ignition system
P0400-P0499 Auxiliary emissions controls
P0500-P0599 Vehicle speed/ Idle control systems
P0600-P0699 Computer output circuits
P0700-P0899 Transmission*
U0000-U2500 CAN codes**


After the trouble code has been identified, you may now start to research the code specifically and learn the general operation of the system the trouble code refers to.

For vehicle specific information you may want to invest in a repair manual or an online vehicle repair subscription.


EXAMPLE: P0115 Engine coolant temperature malfunction.

This code refers to the engine cooling system and therefore any info you can learn about the cooling system for your vehicle would be applicable.

Visual inspection.

Once you feel comfortable with understanding how the vehicle system operates, you can move onto locating the component/system in question. Visually inspect for anything that may indicate a problem, including:

  • Cracks in wires
  • Corrosion
  • Burn marks
  • Loose connectors or terminals
  • Damage from rodents and other pests

EXAMPLE: P0115 Engine coolant temperature malfunction.

Visually inspect the cooling systems components for leaks, and check the coolant level. Use Movi or Movi Pro to watch the coolant temperature PID while the vehicle is running to see what temperature the ECM is seeing. Normal engine temperature should be between 180–220°F (82–104°C) for most vehicles. You may want to compare the ECM temp to the actual temp by using an infrared laser thermometer. If inaccurate you may want to perform further tests on the coolant temp sensor, or check for air in the system.

Pinpoint the problem.

This can be the most time consuming part of the diagnosis process. Sometimes problems can be found easily and quickly and other times you may need to test and re-test every component of the system in trouble. The most important thing is to simplify your troubleshooting process. Many times a simple web search for your code with the year, make, and model can reveal common "pattern failures" that may occur in particular models.


The web search of the problem encountered could allow for a short-cut to the solution, or could be the step for more research and a better understanding of how the component in question works.

It is nearly impossible to fix a component of a system if you don't understand how it works, so a better understanding may be the solution to pinpointing your problem.

Repair and clear the code.

Once a repair has been made, use Movi or Movi Pro to clear the DTC and all related freeze frame data. You may now drive your vehicle through a drive cycle (a drive cycle is different than a key cycle and can take up to two weeks or more depending on how you drive your vehicle and the systems' requirements for a test to complete). You may use Movi or Movi Pro to see if your vehicle has completed a drive cycle by checking to see if all onboard tests show complete.

Once the onboard tests have all completed or at least the system you performed the repair on, and no trouble codes returned, this verifies a successful repair.


Repair and clear the code

Common codes and related repairs

P0300 – P0316 Misfire codes are common and typically relate to the vehicles' ignition system. Beware that engine timing, fuel system faults, and lean/rich conditions can also cause these codes. Common failure items related to these codes would be ignition coils, spark plugs, ignition wires, intake leaks, etc.

P0420 – P0434 Catalyst efficiency codes. These usually indicate failure of the Catalytic Converter itself, however a failed oxygen/AF sensor, exhaust leaks, or wiring faults may also be the root cause. A good test is to use Movi or Movi Pro to monitor the rear O2 (Oxygen) sensor. Watch the voltage at idle* and see if it changes it's voltage like the front O2 sensor does. A normal rear sensor should have a stable voltage between .3 and .8 volts. If the voltage on the rear sensor moves with the front, this indicates there is excessive deterioration in the catalytic converter and it needs replacement.

*Vehicle must be at operating temp. This reference is for a gasoline powered internal combustion engine using oxygen sensors for air/fuel management.

P0400 – P0408 Exhaust gas recirculation malfunctions usually occur from wear of the mechanical valve that is used for EGR function. Many vehicles use multiple components to control this valve, but the valve itself is prone to wear and is a common culprit of related codes.

P0440 – P0459 Evaporative emission control system malfunctions are the codes that relate to the infamous loose gas cap. If one of these codes is present, check your gas cap to ensure it was tightened properly. Also if you live in a state that deals with snow and salt, you may find some rust on the fuel filler neck that won't allow for a proper seal. Once these have been verified and remedied, use Movi or Movi Pro to clear the code/s and perform a drive cycle to see if you need further diagnosis of this system or if it was indeed "just a loose gas cap". The evaporative emissions system is made up of many components and can be time consuming to test all of them. That is why it is easiest to check the gas cap first, then move on if needed.

P0500 – P0504 Vehicle speed sensor malfunctions may be related to a scenario vs. a component. Many vehicles without ABS may only use one wheel speed sensor, this may also be the only wheel spinning if your vehicle is stuck in a snow bank. Ensure you have not had a similar scenario before spending your money on parts or a lot of time diagnosing.

P0128 Coolant thermostat malfunction. This code can be deceiving, however most times it directly relates to the thermostat and replacement may be necessary.

P0171 and P0174 System too lean bank 1 or 2. These codes can be tough to diagnose as many components may be at fault. It's best to check the intake system for any leaks, inspect the air metering device (MAF or MAP), and check the fuel system for proper operation. Sometimes a simple unplugged or broken vacuum line can be the culprit of these codes.

Yhasi is not responsible or liable for any advice provided on this webpage. The advice provided is of a general nature and should be used only as an informational tool and not as a replacement for direct advice from an automotive professional.