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Old 14th June 2021, 01:22   #1
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Default Understanding DTC / OBD2 Codes

Most of us drive our cars to the service centre or an FNG if we have a problem with our car. These folks use a scanner or a laptop to scan for error codes or DTC's at some point in time. Most of us might fret for a DTC, however, the DTC can help in saving time while you're troubleshooting your car. The Check Engine Light would scare even the most prominent technicians and vehicle owners alike.

What's a DTC?

A DTC or a Diagnostic Trouble Code, also known as OBDII codes, are your car’s system for alerting you of vehicle issues. There are typically limits for each system within your vehicle. When the vehicle detects that the issue exceeds these limits, it sends out a trouble code. Most cars post-1996 have an OBD port.

The challenge with this is that every model has different codes and meanings. For instance, a VW won’t have the same codes as a Suzuki. This makes it difficult if you’re reading the codes on your own unless you know the codes for your specific model.

The Four Categories of DTC are:
  • B-codes (body codes): Though body often refers to the outside of the vehicle, B-codes refer to features inside. More include comfort, convenience, and safety features.
  • C-codes (chassis): Functions outside of the passenger compartment including brakes, steering, and suspension.
  • U-codes (network/vehicle integration): Functions shared among the vehicle’s systems and computers.
  • P-codes (powertrain): Include functions such as the engine, transmission, and drivetrain.

DTC codes are five characters long. Each character in the DTC provides a different piece of information about the vehicle’s problem.

Steps to Interpret a DTC:

1. The first character is always an alphabet viz.

P – Powertrain. Includes engine, transmission, and associated accessories.
C – Chassis. Covers mechanical systems and functions: steering, suspension, and braking.
B – Body. Parts mainly found in the passenger compartment area.
U – Network & vehicle integration. Functions managed by the onboard computer system.

2. The second character is a number

The first letter is followed by a number, usually 0 or 1.

0 – Standardized (SAE) code, also known as generic code (sometimes called global)
1 – Manufacturer-specific code (sometimes called enhanced)

The following three digits are purple digits, which may be hexadecimal and correspond to incremented numbers. Typically, the P family codes have sub-families defined by the first digit.

3. The third character is a number

For powertrain codes, this number tells you which vehicle subsystem has a fault. There are eight:

0 – Fuel and air metering and auxiliary emission controls
1 – Fuel and air metering
2 – Fuel and air metering – injector circuit
3 – Ignition systems or misfires
4 – Auxiliary emission controls
5 – Vehicle speed control, idle control systems, and auxiliary inputs
6 – Computer and output circuit
7,8 & 9 – Transmission

You may also see an A, B, or C, which can refer to hybrid propulsion systems.

4.The fourth and fifth characters are numbers

The final piece of a DTC is a number that defines the exact problem that you’re experiencing. It can be a number between zero and 99.

Let's consider an example:

"B0639": This means that the error is from the Body Control Module, Generic issue, Computer and Output Circut and 39 being the actual fault description. the fault number can vary across different manufacturers. In some cases, the checksum for the hexadecimal value might also appear.

An illustrative example:
Name:  obd identify.JPG
Views: 4893
Size:  83.1 KB

Now, let's consider a car make's DTC code(This is easier to identify as they're mentioning the problem and the cause for the problem):
Understanding DTC / OBD2 Codes-example-vw.jpg

Here's a pic of the DTC code from my car's Speedometer:
Understanding DTC / OBD2 Codes-img_20210408_232604.jpg

To access the repository of codes: https://www.dtcdecode.com/

This link has almost all the car manufacturers list except Tata and Mahindra.

Hope this information helps in understanding DTC codes. Have fun solving your car's codes(I hope these instances do not occur though).

Last edited by jithin23 : 14th June 2021 at 01:33. Reason: Attaching pic
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Old 14th June 2021, 04:17   #2
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Default re: Understanding DTC / OBD2 Codes

Thanks for the thread. I have an Ancel OBD2 scanner. As I drive two Land Rovers, I am paranoid about knowing what is going on inside the vehicles So here is the setup, though thankfully there has been no DTCs in either of the vehicles, yet!

Understanding DTC / OBD2 Codes-767feabc7006441a9deb3efc4e671f2e.jpeg
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Old 14th June 2021, 05:26   #3
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Thread moved out from the Assembly Line. Thanks for sharing!
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Old 14th June 2021, 07:18   #4
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Default re: Understanding DTC / OBD2 Codes

Quote:
Originally Posted by jithin23 View Post
The Check Engine Light would scare technicians and vehicle owners alike.

Typically, the P family codes have sub-families defined by the first digit.
Short but sweet topic to kickstart a very healthy technical discussion.

When OBD II scanners arrived, people would make a big deal of it, and even now, it is so in India. However, overseas, a decent mid-budget scan tool with the capability to perform all systems diagnosis, oil Reset, EPB, SAS, BMS, DPF, Throttle A/F are available for as low as 250USD. That is like the money one would spend on a mid-budget smartphone. I was targeting an Autel scan tool but shelved the plan in Mar-2020 due to the current situation. In India, we have caRPM but there are some strings attached about yearly subscription charges.

I've seen DTCs on my Grand Vitara twice - one with a transmission error, and the other, a stored DTC but without the CEL on. Both, shown below, were eventually linked to clipped wires thanks to rats . The third one shown below is of the DSG of a VW GT TSI, still unsolved.

P2764 - Transmission Torque Converter Clutch related
Understanding DTC / OBD2 Codes-errorcode.jpg

P0463 Fuel Sensor related
Understanding DTC / OBD2 Codes-errorcode_fuelsensor_gv_apr2021.jpg

P177C, P1725, P176F DSG Clutch on a VW Polo GT TSI (Unsolved yet)
Understanding DTC / OBD2 Codes-errorcode_transmission_vwpologttsi.jpg

Last edited by vigsom : 14th June 2021 at 07:27. Reason: updating info on scan tools
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Old 14th June 2021, 07:35   #5
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Default re: Understanding DTC / OBD2 Codes

I have a P 0037 and P 0443 on my Altis and hence the Check Engine Light. While I know the reason behind P 0037, and that is no oxygen sensor, I don't know the reason for P 0443. I had removed the EVAP canister valve and fit it back but the code persists.
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Old 14th June 2021, 09:12   #6
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Default re: Understanding DTC / OBD2 Codes

I have an ELM 327 Scanner which I connect wirelessly and use the Car Scanner App on my phone to get the error codes. The app is Pretty good to get most of the basic codes and clears them too, however there is no service reset available through it, the connection often drops and you have to try reconnecting it through WIFI a couple of times.


Used it to detect ABS Speed sensor errors on my Volvo V40, I firstly cleared the codes to check if it comes up again and indeed it did, so I ended up changing the sensor.

This is a pretty basic set up, I dont mind investing in something better which can read various other codes, ECU codes and reset the Service Intervals. Open to any suggestions.
Attached Thumbnails
Understanding DTC / OBD2 Codes-photo20210321084346.jpg  


Last edited by Y@SH : 14th June 2021 at 09:13.
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Old 14th June 2021, 11:03   #7
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Default re: Understanding DTC / OBD2 Codes

When you are in the market for an OBD scanner look for at least two things

Will it scan manufacture specific codes, so not just P0 codes, and will it scan other than P codes.

Many generic code readers will only scan P0 codes. Whereas that is a great start, you really want to be able to scan manufacturer codes. There are many more of those. Also being able to scan more than the P code can be a great help.

Jeroen

Last edited by SDP : 15th June 2021 at 15:43. Reason: Minor typo
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Old 14th June 2021, 11:05   #8
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Default re: Understanding DTC / OBD2 Codes

Quote:
Originally Posted by BlackPearl View Post
Thanks for the thread. I have an Ancel OBD2 scanner. As I drive two Land Rovers, I am paranoid about knowing what is going on inside the vehicles So here is the setup, though thankfully there has been no DTCs in either of the vehicles, yet!
Sure, happy to help the community! We'll that's one good setup you have for the DTC's, can be diagnosed quickly any time if any issue pops up.

Quote:
Originally Posted by vigsom View Post
Short but sweet topic to kickstart a very healthy technical discussion.

When OBD II scanners arrived, people would make a big deal of it, and even now, it is so in India.
I was targeting an Autel scan tool but shelved the plan in Mar-2020 due to the current situation. In India, we have caRPM but there are some strings attached about yearly subscription charges.

I've seen DTCs on my Grand Vitara twice - one with a transmission error, and the other, a stored DTC but without the CEL on. Both, shown below, were eventually linked to clipped wires thanks to rats . The third one shown below is of the DSG of a VW GT TSI, still unsolved.
Thanks and Absolutely! In India most if the mechanics too make a big deal for a DTC code. As you mentioned an Autel scanner can do wonders in car diagnosis, though importing is the biggest challenge for us in India now. Even sites like eBay do not ship to India. I'm nor sure about carpro and it's functions though.

Rat bites in my car's engine bay were one of the reasons to find out more on DTC's because the rats would make the engine bay their home even though I used to change parking spots. Thankfully by changing the affected wires, the DTC was gone.

VW's have an affinity for DTC's, however on the flipside, they're fun to drive.

Quote:
Originally Posted by Swapnil4585 View Post
While I know the reason behind P 0037, and that is no oxygen sensor, I don't know the reason for P 0443. I had removed the EVAP canister valve and fit it back but the code persists.
Here you go for the P0443 DTC. Hope this helps.

Understanding DTC / OBD2 Codes-screenshot_20210614105144.jpg
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Old 14th June 2021, 15:49   #9
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Default re: Understanding DTC / OBD2 Codes

Quote:
Originally Posted by Jeroen View Post
When you are in the market for an OBD scanner look format least two things

Will it scan manufacture specific codes, so not just P0 codes, and will it scan other than P codes.

Many generic code readers will only scan P0 codes. Whereas that is a great start, you really want to be able to scan manufacturer codes. There are many more of those. Also being able to scan more than the P code can be a great help.

Jeroen
Adding to the point above, one can get an ELM327 OBD cable and use Manufacturer specific applications such as Forscan or VCDS to get a better insight about their vehicle. The DTC's are more detailed in these applications.

Here's a pic for the DTC in Forscan
Understanding DTC / OBD2 Codes-img_20210523_140749__01.jpg

Similarly there's another application called TOAD Pro(Total Car Diagnostics). This software performs all dealer level functions to your car and covers almost all the car brands. Equivalent to Forscan/VCDS.

This is the website link for toad though the page looks outdated.
https://www.totalcardiagnostics.com/toad/

Other softwares which are brand specific are HiCom/GDS/KDS/G-scan(For Hyundai-Kia cars), Jscan(for Jeep), SDT(For Suzuki and Maruti Suzuki).

Tata has a separate software to be purchased from https://ed.tatamotors.com/frmproductlist.aspx

Quote:
Originally Posted by Y@SH View Post

I dont mind investing in something better which can read various other codes, ECU codes and reset the Service Intervals. Open to any suggestions.
As vigsom suggested, you can go for Autel. It's good and has a comprehensive set of functions and can help in clearing errors. Starts at 5k INR on Amazon.

Last edited by Aditya : 15th June 2021 at 16:39. Reason: As requested
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Old 15th June 2021, 10:09   #10
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Default Re: Understanding DTC / OBD2 Codes

Thanks for putting up this DTC code decoder. Before this I though it is just a random manufacturer specific number.

I got the following codes
  • P0101
  • P1525(F3)
  • P0101(22)
while on a highway drive after a long break.

Quote:
Originally Posted by Tgo View Post
Update on the Green One

I was driving on the e-way on a Sunday and realized that I haven't given the car an Italian Tune-up in a long while. Also wanted to check whether the tyres need a balancing or not. Carefully placing myself in open sections without traffic I started gunning it. in the third pass, this happened. and I lost Cruise Control.


Was quite troubled as I didn't know what to do or why it happened. Stopped in the service lane. Shut down the car after idling for a minute. Opened the bonnet and checked the coolant flash tank which had the correct level. Checked the engine oil, which was also at the right level. Saw some oil on the intercooler which is a result of the intercooler hose design. A lot of cars have this problem and it seemed normal. Checked the air filter and it also seemed to be intact. Got back in the car and drove for another 2 hours to reach the destination. There was no difference in the way the car performed, no limp mode or abnormal noises. Just that Cruise Control was not functioning. Hence kept driving cautiously and eventually settle into the natural driving rhythm.

Before beginning the return journey, I checked the manual which said that the light was glowing Amber and there was no need to stop driving. It needs to be driven to the nearest ASC for a check-up. Couldn't do that on the way back as Renault-Etawah was closed that day. Lived with the anxiety for the next week or so and ordered a OBD-II scanner for the first time. This is the fault code summary I got off the first scan report of the vehicle.


Was able to clear the code and it hasn't showed up again. Will get it checked at the ASC in the next visit. I am guessing it is something to do with EGR or MAF sensor. The EGR valve might be needing a clean-up.
It finally got cleared and has not reoccurred after replacement of the intercooler which was leaking from the collector nozzle and the hose connection to the intercooler.

My guess is there was some oil build up in the intercooler from past turbo failure or the leak from the places mentioned which was resulting in a deviation in the data table that the ECM tallies.
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Old 15th June 2021, 11:01   #11
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Default Re: Understanding DTC / OBD2 Codes

Quote:
Originally Posted by jithin23 View Post
*SNIP*

To access the repository of codes: https://www.dtcdecode.com/

This link has almost all the car manufacturers list except Tata and Mahindra.

*SNIP*
Hmm... when I click on that link (or manually type the URL) in any browser, all I get is an empty page with just the logo of DTCDecode.com at the top and links at the bottom for rtivacy Policy, Contact Us and Terms.

This is on a desktop computer (Mac) wiith Firefox, Safari and Opera browsers.

Edit: I tried the same thing on an iPhone with Safari, same results.

Cheers
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Old 15th June 2021, 11:09   #12
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Originally Posted by tilt View Post
Hmm... when I click on that link (or manually type the URL) in any browser, all I get is an empty page with just the logo of DTCDecode.com at the top and links at the bottom for rtivacy Policy, Contact Us and Terms.

This is on a desktop computer (Mac) wiith Firefox, Safari and Opera browsers.

Edit: I tried the same thing on an iPhone with Safari, same results.

Cheers
Even I tried accessing the link today and it works fine on Google Chrome on desktop. Try clearing the browser cache and try again. Hope it helps

Here's a pic. Took this just now
Understanding DTC / OBD2 Codes-img_20210615_111042__01.jpg

Last edited by jithin23 : 15th June 2021 at 11:14. Reason: Adding pic
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Old 16th June 2021, 14:47   #13
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Default Re: Understanding DTC / OBD2 Codes

All

I have a MJD Linea - MY 2009, BSIII
Can anyone guide me to the specific OBD device that is compatible with this car, to read / identify fault codes.
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Old 16th June 2021, 15:36   #14
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Thanks for this. I've been playing around Torque for some time now to push data to my home automation system with a vgate BLE 4.0 OBD 2 adapter
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Old 16th June 2021, 17:32   #15
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Default Re: Understanding DTC / OBD2 Codes

I have a VGate OBD adapter and have scanned my XUV for any error codes. I got a U1001 error but there is no warning light and the vehicle performs just like it did on day 1. Is this something I should be worried about?
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