standard dtc
Vehicle maintenance

Understanding Standard DTC Codes: Common Fault, Causes & Fixes

Written by

What Are Diagnostic Trouble Codes (DTC)

The DTC Codes are warning to a vehicle user that there is a problem that needs to be fixed as soon as possible. These codes are contained in every vehicle, there’s no vehicle whose computer does not diagnose issues and faults. The Diagnostic Trouble Codes (DTC) were designed by Society Automotive Engineers (SAE) for easy maintenance and repairs.

It is left for the driver to find these codes when the vehicle warning sign are displayed on the dashboard, so as to get it to a mechanic as soon as possible. Some drivers might keep on driving even with these warning symbols either on of flashing on the car dash. Please avoid this attitude. Though the vehicle is not totally broken, it will break down if the necessary attention is not given to it in terms of repairs. You can even get a diagnostic check for free for your vehicle if you know where to find one

These codes are divided into 2 main parts. The Manufacturer’s specific and the standard dtc codes.

How To Interprete DTC Codes

how to understand dtc codes

NOTE: There are banks which are associated with these codes, it helps the driver to know the side of the vehicle where the fault is detected. For instance, the bank 1 and 2 tells if the vehicle’s issue is from the left hand side or the right hand side.

The position of bank one determines that of bank 2. Bank one is located wherever cylinder 1 is located while bank 2 takes the other side. If bank 1 is in driver’s side then bank 2 will be at the passenger’s side, vise versa

Common Standard DTC: Codes, Causes And Fixes

While the diagnostic trouble codes displayed on your OBD2 scanner may vary depending on the car’s problem, make, year, and model; here are some common standard DTC codes that correspond with most cars:

Since most standard diagnostic trouble codes start with P, we will be considering only those in this category.

P0100 – P0199 (Fuel and Air Metering)

Diagnostic trouble codes in this category are used to monitor the air and fuel ratio of the car’s engine to indicate failing oxygen sensor(s). They also help to keep a check on a car’s emission and fuel economy.

Common codes in this range include:

1.                  P0135 & P0141 (Oxygen Sensor Heater Circuit Malfunctions)

The P0135 trouble code is a generic powertrain code signifying problems in the Oxygen Sensor 1 on Bank 1. These heated oxygen sensors reduce the time taken by the engine to enter a closed loop, which helps to reduce emissions and increases fuel economy and overall engine performance. It can trigger the reduced engine power warning symbol.

P0141 indicates problems in the Oxygen Sensor 2 on Bank 1, a heated oxygen sensor that ensures proper heat maintenance for efficient catalyst monitoring.

Possible Causes

  • High resistance in the oxygen sensor heater control circuit wiring or element.
  • High resistance in the oxygen sensor heater ground circuit.
  • Wiring harness short to ground or open.
  • Open heater element or internal short.

When you start your car engine, and any of these is detected, the OBD II system will send P0135 or P0141 trouble code.

How to Fix These Problems

Fixing problems involving the 02 Sensor heater requires electrical or rewiring expertise. If you’re inexperienced in repairing automotive electrical systems kindly save yourself time, stress, and money by taking your vehicle to a dealer or mechanic.

However, depending on your level of experience, you can save yourself some money by carrying out the necessary testing, repair, or replacement yourself.

2.                  P0171 & P0174 (System Too Lean)

P0171 & P0174 trouble codes indicate that the Air-Fuel Ratio Sensor has detected a lean fuel mixture in Bank 1(P0171) or Bank 2(P0174) of the car engine. The ideal air-to-fuel ratio in the engine is 14.7: 1. When there’s an imbalance in the ratio; say, too much air or too little fuel in the engine, any of these codes will be sent to indicate the problem.

Possible Causes

  • Vacuum leaks in gaskets of hoses
  • Clogging or faulty fuel filter
  • Hesitating or surging acceleration
  • ECR system issues
  • PCV system leaks
  • Worn fuel pump
  • Mass airflow sensor

Any of the causes listed above can result in a lean fuel mixture, and when this happens, any of the codes will be sent to indicate the problem.

How to Fix These Problems

The P0171 and P0174 are not usually regarded as emergencies. You can continue driving your car while preparing to fix the issue. However, don’t wait too long to get the repair done, a lean fuel mixture in the long term can lead to engine overheating and severe internal damage.

Take your car to the mechanic if you’re not experienced in air-fuel metering system repair and maintenance – but if you know a thing or two about it, follow the steps below to get your car back in order

  • Scan your vehicle for the trouble code to ensure it is a MAF (mass airflow ) sensor problem.
  • Inspect the hoses and vacuum lines in your engine for leaks, tears, or cracks. Also, be sure that all connections are intact.
  • Take out the MAF sensor and clean it with a brake cleaner or MAF cleaning spray.
  • Reinstall the sensor, ensure all leaks, crack, tears, and loose connections are fixed.
  • Clear the DTC codes and scan your vehicle system again.

P0200 – P0299 (Fuel and Air Metering – injection circuit)

Diagnostic trouble codes in this range are usually sent when there’s a problem with the fuel injector. Common codes in this range include:

1.                  P0200 (Injector Circuit Malfunction)

The P0200 trouble code is sent when the OBD II system detects a malfunction or problem in the fuel injection circuit. The fuel injector is controlled by the fuel injector circuit, it determines when to spray the fuel and how much of it is sprayed.

Possible Causes

  • Shorted or Open injected
  • Grounded driver circuit
  • Faulty PCM (Powertrain Control Module)
  • Poor electrical connection
  • Failing or failed injector

How to Fix This Problem

  • It’s pretty easy and straightforward to repair this trouble code problem. The cause of the problem can be identified through diagnosis
  • Replacement of the PCM
  • Replace the fuel injector
  • Replace or repair any wiring issues.
  • Replace or repair any connection issues.

2.                  P0218 (Transmission over Temperature Condition)

This is a trouble code that means “Transmission over Temperature”. The P0218 means that the transmission temperature has exceeded the maximum temperature allowance limit set by the car manufacturer.

Possible Causes

A part of the transmission system may be faulty. This could be the radiator, transmission cooler, transmission cooler line, or transmission pan.

  • Excessive friction between moving transmission parts due to faulty internal transmission.
  • A faulty PCM or transmission temperature sensor
  • Engine overheating

How to Fix This Problem

If you can, carry out the necessary diagnosis to determine the problem. Otherwise, take your car to the mechanic for the diagnosis. The following repairs or replacements can put your car back in order:

  • Replace the vehicle thermostat
  • Replace the coolant temperature sensor
  • Replace any faulty transmission part to eliminate transmission fluid leak
  • Repair engine overheating
  • Replace the entire transmission system.

P0300 – P0399 (Misfire or Ignition System)

The trouble codes in this range are sent when there’s a problem with the vehicle’s ignition system. E.g. spark plug

Common codes in this range include:

1.                  P0300 (Multiple/random Cylinder Misfire Detected)

Trouble codes in this range are sent when one or more engine cylinders are misfiring. P0300, P0301, P0302, P0303, P0304, are some of the most common trouble codes for misfiring cylinders. The last digit of the code signifies the particular cylinder that’s misfiring. For example, P0303 indicates that cylinder 3 misfire is detected.

Possible Causes

  • Worn or damaged spark plug(s)
  • Worn or damaged spark plug wires
  • Damaged or worn roto button
  • Low fuel pressure
  • Faulty crankshaft sensor, camshaft sensor, or MAF sensor
  • Faulty fuel pump or injector

How to Fix This Problem

P0300 trouble code and other related error codes should be treated as an emergency and should therefore be repaired immediately. Carry out the necessary diagnosis to figure out the cause of the problem and repair or replace as appropriate

2.                  P0325 (Knock Sensor 1 Circuit Malfunction – Bank 1)

The P0325 is a diagnostic trouble code sent by the OBD II system when a problem is detected in the knock sensor circuit. This code is sometimes sent alongside other knock sensor codes and lean mixture codes.

The P0325 means there’s a fault in the knock sensor 1 on bank 1. When the OBD II system does not receive the appropriate info from the knock sensor, it will trigger the Check Engine Light and send the corresponding DTC to indicate the source of the problem.

The knock sensor informs the car computer when there’s knocking among the engine’s cylinders, i.e., exploding the air-fuel mixture such that less power is delivered to the engine.

Possible Causes

  • A faulty Knock Sensor
  • Faulty knock sensor wiring
  • Faulty or failed PCM

How to Fix This Problem

Problems with the knock sensor are not serious one. You can carefully drive our car to a safe location or the mechanic workshop for diagnosis, repair, or possible replacement.

  • Check knock sensor resistance
  • Check for faulty or broken wires connected to the sensor
  • Observe for fault or misconnection in the wires from the PCM to the knock sensor circuit.
  • Replace the knock sensor

P0400 – P0499 (Auxiliary Emission Controls)

The trouble codes in this range are used to indicate problems with the evaporative emission control system (EVAP). The primary function of this system to prevent the release of gas fumes into the atmosphere, thereby helping to reduce air pollution.

Common codes in this range include:

P0401 (Exhaust Gas Recirculation Flow Insufficient Detected), P0411 (Secondary Air Injection System Incorrect Flow Detected), P0420 (Catalyst System Efficient Below Threshold – Bank 1), P0430 (Catalyst System Efficient Below Threshold – Bank 2), P0440 (Evaporative Emission Control System Malfunction)

P0401 (Exhaust Gas Recirculation Flow Insufficient Detected)

This code is sent when there’s insufficient flow of EGR within the EGR valve when it is supposed to open the flow of Nitrogen Oxide gases into the manifold. The EGR has three special parts – the EGR valve, differential pressure sensor (DPFE), and the actuator solenoid.

Possible Causes

  • The DPFE may be faulty
  • Faulty EGR valve
  • Failure of the EGR valve to open due to low vacuum
  • Carbon build-up in the EGR tube, leading to blockage of the valve.

How to Fix This Problem

  • Open the blocked EGR valve with a vacuum pump and keep an eye on the RPM engine and DPFE voltage.
  • Clean the EGR valve to remove any blockage or deposits
  • Replace the EGR valve
  • Replace the DPFE sensor

P0500 – P0599 (Vehicle Speed Control Idle and Idle Control System)

Trouble codes in this range are sent by the OBD II systems when there’s a problem with the vehicle speed sensor. P0500 and P0505 are the common codes in this range, and they are used to monitor the vehicle’s idling and speed controls.

P0500 (Vehicle Speed Sensor Malfunction)

The P0500 trouble code is sent when problems (such as lack of signal or incorrect speed reading) have been detected in the vehicle speed sensor circuit.

The speed of a moving vehicle is displayed by the speedometer. But for the speedometer to be accurate in its reading, correct info must be supplied by the vehicle speed sensor.

Possible Causes

  • The PCM may be faulty
  • Faulty vehicle speed sensor
  • Faulty drive gear
  • Faulty electrical connection
  • The PCM may not be configured for the vehicles tire size

How to Fix This Problem

Since there are several possible causes of this problem, it is better to take your vehicle to a mechanic workshop for proper diagnosis, repair, and possible replacements.

  • Repair faulty electrical connections
  • Replace damaged VSS
  • Replace VSS drive gear

P0600 – P0699 (Computer Output Circuit)

DTC codes in this range would be sent when your vehicle’s computer system is malfunctioning. Common trouble codes in this range include P0600 (Serial Communication Link Malfunction, P0602 (Control Module Programming Error), and P0604 (Internal Control Module RAM Error).

P0600 (Serial Communication Link Malfunction)

This error code is used to indicate a  malfunction in the ECU’s communication link. This implies that the electronic control unit/module (ECU/ECM) has lost connection with one or more of its controllers multiple times. The Check Engine Light is turned on and the P0600 trouble code is sent by the ECU when this dysfunction is detected.

Possible Causes

  • Failed ECU
  • Low voltage in the car battery
  • Electrical misconnection in the ECU

How to Fix This Problem

The ECU is one of the most important systems in your car; therefore any attempt to DIY may cause your wallet to suffer severe consequences. ECU malfunction will require careful diagnosis or troubleshooting by a mechanic or an expert in-vehicle electronic and computer systems to ascertain the cause of the problem.

The P0600 trouble code is a serious malfunction and should be treated as such, as it can affect other systems in the car, leading to defect in normal operation.

  • Repair of electrical misconnections
  • Replacement of the ECU
  • Repair or replace the wiring harness of the ECU
  • Diagnosis and repair of the cause of the battery’s low voltage.

P0700 – P0899 (Transmission System and Others)

The diagnostic trouble codes in this range are used to monitor and indicate malfunctions in the transmission system. P0700 (Transmission Control System Malfunction) and P0702 (Transmission Control System Electrical) are the most common codes in this range.

P0700 (Transmission Control System Malfunction)

The P0700 is a generic trouble code sent by the OBD II system when it detects a malfunction in the transmission control system. When this happens, the Check Engine Light will come on, the engine may run poorly due to transmission shifting problems. Proper diagnosis will reveal the root of the problem.

Possible Causes

  • Defect in the transmission system
  • Low level or dirty transmission fluid
  • Faulty TCM (Transmission Control Module)
  • Faults in the engine coolant sensor
  • Faulty shift solenoid

How to Fix This Problem

  • Replace the TCM
  • Repair or replace defective wiring
  • Replace the valve body
  • Replace the Transmission shift solenoid
  • Replacement of the transmission fluid

The P0700 trouble code shows a defect in the transmission system and hence should be taken seriously. Take the car to a mechanic for proper diagnosis, repair, and possible replacements.

Final Thoughts

The DTC Codes vary from vehicle to vehicle and from vehicle model to another. Apart from the common codes applicable to all vehicles, it is important to make use of the vehicle’s user manual to be able to understand the vehicle’s dashboard warning signs. The earlier a driver detects these trouble codes and takes the vehicle for repair, the better it is to extend the lifespan of one’s vehicle.

Watch Video: OBD II Connector & Fault Codes Explained