OBD2 Troubleshooting Guide

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Before you give up and drive your car to the shop because you can't find any OBD (on-board diagnostic) codes on your car's computer, there are a few things you should check.

You're already ahead of the game if you know how to utilize your car's OBD system, but let's review the diagnostics, error messages, scan ports, and other features of the OBD-II code.

Table Of Content

  1. What is OBD (On-Board Diagnostics)?
  2. How do you troubleshoot an OBD scanner that won't turn on?
  3. 4 OBD scanner plugs that are damaged
  4. How to troubleshoot OBD scanner connection issues
  5. What is Mercedes OBD and what can it do for you?
  6. Conclusion

1. What Is OBD (On-Board Diagnostics)?

Vehicles have had a built-in troubleshooting mechanism known as OBD since the mid-1990s. A computer in your car monitors sensors that detect engine temperature, exhaust gas mixture, and other variables that, unless you're a serious automotive troubleshooter, would be meaningless to you.

OBD2 Troubleshooting Guide

The computer in your car or truck regularly analyzes these sensors to ensure that the values they measure are all within the manufacturer's recommended or safe range. If they deviate from that range, the computer records it and stores it as an error code. Hundreds of error codes can be found in a modern car, each indicating a different problem.

These codes can be accessed by a mechanic, whether a professional or a qualified do-it-yourselfer, to assess the engine's overall health.

This is accomplished by connecting a scan tool to a computer-style port on your vehicle (the location of which will be indicated in your repair handbook) and downloading the codes.

OBD2 Troubleshooting Guide

Then you may look up the codes on a website like OBD-Codes.com to see what they mean. Most car parts chain retailers will scan your codes for free.

2. How Do You Troubleshoot an OBD Scanner That Won't Turn On?

It's a little concerning to plug in your scanner and discover it doesn't work; some of these instruments are costly. But don't be alarmed; we'll figure it out. This can happen to you a lot of times, and it's never because of the scanner.

A blown fuse on the vehicle's OBD socket power supply circuit is the most typical reason for an OBD scanner that won't switch on. If the check engine light does not illuminate, the fuse has most likely blown. The problem can be resolved by checking the fuse box and replacing the blown fuse.

You'll discover all about the most common causes of a scanner that won't switch on, how to diagnose them, and how to fix them in this article.

OBD2 Troubleshooting Guide

2.1 Blown OBD Socket Fuse

plugging in the scanner to find it won’t power up is a relatively common error. The DLC (Data Link Connector), often known as the OBD port or socket, delivers power to your scan instrument.

When your tool loses power, it's likely because the vehicle's OBD socket isn't receiving electricity. When the check engine light goes out, you know you've figured out why your scan tool won't turn on.

The most typical cause of the loss of electricity at the socket is a blown fuse. If this is the case, replacing a blown fuse will only take five minutes and the OBD will be operational once more.

2.2 How Do You Locate The OBD Fuse?

The OBD fuse usually blows because the circuit is overloaded. Because the OBD fuse is frequently shared with the cigarette lighter, 12-volt socket, or other consumers, this is the case. The fuse may blow if you plug in a broken accessory, such as a phone charger, or if you use high-power equipment, such as a fan.

OBD2 Troubleshooting Guide

So, if your 12-volt port/cigarette lighter is likewise not working properly, then you have probably located the source of the problem.

Multiple fuse boxes are likely to be installed in your vehicle, with three being the most common. There's one under the hood, one in the trunk, and one behind the steering wheel.

The OBD fuse may be labeled OBD II, DLC, Accessory port, 12-volt PowerPoint, or cigarette lighter on the fuse cover and is most likely located inside the vehicle.

Checking the driver's manual is the most efficient approach to find it. Many decent drivers manuals will give the fuse location, kind, color, rating (size), and a description of what it powers under the heading "fuses."

2.3 Examining The OBD Fuse

Fuse testing can be done in three ways:

  • Using a test light.
  • A voltmeter to measures the voltage.
  • Check the conductive strip after removing the fuse.

Pulling the fuse is the quickest method. A blade-type fuse is used in most fuse boxes, and while it is easy to remove, it is small and tough to hold. Frequently, a useful tool is clipped to the back of the fuse box cover.

OBD2 Troubleshooting Guide

Pull the fuse body with the tool hooked over it. Holding the fuse to the light reveals the strip; replace the fuse if it's damaged.

Never assume the removed fuse size is the correct size; always check the rated fuse in the driver's manual. They are frequently not, and replacing a fuse with one that is rated below spec will result in the fuse blowing again.

Fitting a fuse that is larger than recommended may cause damage to components or, in the worst-case scenario, cause an electrical fire. The most typical fuse size is 15-20 amp, but use the manufacturer's recommendation.

2.4 Open DLC Power Or Ground

If the fuse is fine, a damaged OBD socket is the next most likely cause of no power. It's very frequent in older cars. That makes sense; as the OBD port is used more frequently, the delicate terminals wear out or lose tension.

OBD2 Troubleshooting Guide

The tool will not be powered if the DLC power terminal does not establish solid contact with it.

2.5 Examining Damage To The OBD Socket

Two checks can be done on OBD to see if there's any damage related to this issue.

First, it is important to inspect the port and the port terminals using a flashlight. Examine the terminals to check if terminals 4 and 16 appear to be larger than the rest.

OBD2 Troubleshooting Guide

Terminals 4 and 16 are for chassis ground and power, respectively. These two terminals are needed to turn on your scanner and are the most crucial ones to look at right now.

In the workshop, a test probe can be done to check for spreading by dragging test tension on the terminals. A fine mental tool can help to tighten the terminal legs if the tension is low. Unless you observe a clear terminal spread, it is not recommended to stick anything into the front of the DLC.

A test light or voltmeter will be required for the second inspection.

Both the power and ground routes will be tested. Whether you don't receive a reading on the voltmeter or the test light, try each component separately to see if power or ground is absent.

OBD2 Troubleshooting Guide

It's better to back probe the DLC terminals, although I understand how difficult that can be. Alternatively, gently explore with a paperclip or something like that.

If either path has a problem, look under the dash panel for any damaged wiring. The most vulnerable region for damage is right beneath the dash, where things may collide with the wiring.

3. 4 OBD Scanner Plugs That Are Damaged

Last on the list is scanner damage though they are very resilient and can last for years. It is, nonetheless possible that they can get damaged. A damaged or worn-out scanner cable is more likely to cause a communication failure.

3.1 Examining The Scanner's Plug

Check the pins on the scanner plug; they should be straight and positioned properly. Bending a pin prevents it from making contact with the vehicle's port. The good news is that the cable is universal and replaceable.

OBD2 Troubleshooting Guide

Whether the cable appears to be in good condition, try plugging it into a donor vehicle to see if it works. This confirms that the scanner is the source of the problem.

3.2 Examining The Scanner's Fuse

The scanners are all fused, and the bottle kind is the most popular. It may not be as simple as checking a car fuse to gain access. To check and replace the fuse, the scanner may need to be opened. Consult the maker about the procedure.

3.3 Port Are Clogged With Debris

Another explanation for no reading is that the scan port has filled up with dust after years of inactivity. You shouldn't use a spray cleaner or anything else that can get the port wet, but wiping it down with a soft cloth or blowing compressed air across it might help clear away anything that's blocking your scan equipment from receiving a proper result.

OBD2 Troubleshooting Guide

If one of these remedies works and you now know what codes your vehicle is storing, you can take your vehicle to the shop or your garage for maintenance. If not, a trip to the store might be your best option.

4. How To Troubleshoot OBD Scanner Connection Issues

This section outlines some of the causes as well as what you can do to fix any communication issues between your OBD scanner and your vehicle.

Communication problems can be caused by several factors, including ignition-key position, connector-voltage issues, wrong communication protocol, hung ECM, missing or faulty data, and OEM-updated ECM software that the scan tool is unaware of. We go over some of them in greater depth below.

4.1 Compatibility With OBD Scan Tools

While most OBD code readers should be able to communicate with cars that use the standardized OBDII protocols - or cars that use an OBD2 compatible protocol to cover the engine/emission management system - a common communication issue is when the car you're trying to connect uses a non-standardized OBD protocol like ALDL, MOBD, MUTT, or OBD1.

OBD2 Troubleshooting Guide

These manufacturer-specific protocols necessitate the use of a scan instrument and software capable of reading PIDs. To diagnose a wider range of automobiles and systems, a professional multi-system diagnostic scanner with OBD1 and OBD2 compatibility would be necessary.

4.2 The Ignition Key Is Not In The "Run" Position

The ignition key must be in the run position or the engine must be running to use most OBDII scan instruments. Furthermore, many vehicles require several seconds for all modules to complete their boot-up routines.

OBD2 Troubleshooting Guide

After all, the chimes have finished and all dashboard action has been completed, it's a good rule to use the scan function. If you do not wait for the entire system to load up, the scan tool may not connect to the OBDII system.

4.3 Low Or No Voltage On The Connector

Every OBDII connector is required to provide 12-volt power on pin 16 and ground on pins 4 and 5. The scan tools rely on the presence of this power. To begin, turn the ignition key to the run position.

Place the red/positive lead on pin 16 and the black/negative lead on pin 4 or pin 5 of a voltmeter set to detect DC voltage. 12-volt DC should be displayed on the voltmeter (or near to it). Some scan instruments have trouble connecting if the reading is significantly lower than 11 volts. If this is the case, start by looking at the battery and/or charging system.

OBD2 Troubleshooting Guide

If there is no voltage between the pins, the problem is most likely a blown fuse. Typically, the DLC power is shared with the fuse panel's accessory power. Locate the fuse panel using the owner's manual as a guide and check to see if any fuses have blown. If this is the case, replace the fuse and double-check your power.

4.4 A Hang In The ECM Communication

The ECM can occasionally enter a 'hang' state, in which it functions but does not communicate. The car is operational, but the scan tool indicates that the communication link is unavailable.

OBD2 Troubleshooting Guide

The ECM may need to be rebooted if all other tests have been verified. Disconnect both battery leads and then apply the brake pedal to drain any capacitors in the system to restart the ECM. The entire ECM reboots after the battery are reconnected, and it should begin to communicate again. Consult the vehicle's owner's manual for instructions before disconnecting the battery.

4.5 A Missing Or An Invalid Data

The majority of scan tools connect to the car and query the ECM for valid PIDs. Some scan tools consider the most recent car connected to be the most recent vehicle. As a result, the PIDs might not match. As a result, some PIDs may appear to be unavailable when assessing data.

OBD2 Troubleshooting Guide

Scanning tools allow you to query for PIDs to solve this problem. Depending on the vehicle, this process could take a minute or more. The PID list should match the car when finished, and the data should be correct. Some scan tools do not scan the PIDs automatically, instead of relying on the vehicle's VIN to decide which PIDs are legitimate.

As a general guideline, look for PIDs to ensure that the scan tool is returning the same information as the ECM. It's certainly worth the minute it takes to double-check that the scan tool has the right data.

5. What Is Mercedes OBD And What Can It Do For You?

An OBD diagnostic equipment for Mercedes-Benz vehicles allows you to read error codes from the complicated computerized system's fault memory. Various problem codes referring to various systems and locations of the vehicle are stored in the fault memory.

OBD2 Troubleshooting Guide

These codes reflect flaws or deficiencies in the region in question. There is a distinction made between generic error codes that apply to all makes of cars and manufacturer-specific error codes that are unique to each manufacturer.

Not only can an OBD device designed exclusively for Mercedes-Benz automobiles read general error codes, but it can also read manufacturer-specific error codes. This provides a more comprehensive picture of the vehicle's overall health and state.

OBD2 Troubleshooting Guide

6. Conclusion

OBD is a weird item that appears to work through black magic for many vehicle users. You watch as the workshop employee plugs in this serious-looking gadget and reads some cryptic codes before informing you what's wrong, what has to be done and clearing the codes.

The OBD II is not quite as strange as it may seem. You can check and analyze the codes yourself, evaluate the health of your car's systems, and even check for mileage manipulation using your own Mercedes OBD2 scanner.