Other Articles - January/February - 2020

Where Did Those Extra Numbers Come From? A Look at 7 Digit DTC Diagnosis

For more than 50 years, the EPA (Environmental Protection Agency) has been in charge of making sure the vehicles you repair meet all the federal emissions and fuel economy standards set forth by the federal government. The liaison between the EPA, the US department of Transportation (DOT) and the automotive/ truck manufacturers is an engineering organization known as SAE (Society of Automotive Engineers). SAE is comprised of engineers from all of the automotive and truck manufactures. The SAE groups work with the government to establish the standards (safety, fuel economy and emissions) for the cars and trucks you and your customers own.

SAE develops lots of standards for all vehicles and a lot of them are related to the diagnostics and service for the vehicles you are working on. The “J” standards will typically be referenced by a letter and number format. As and example the J2534, is the standard for aftermarket reprograming, J1850 the data bus design, J1962 standardized the DLC which you use to connect your scan tool to the vehicle. There are a ton of “J” standards with some being very important to vehicle service and some more focused on the engineering end of the vehicle. In 1996, major changes were made to the diagnostic protocols used by the vehicle manufacturers. Known as OBD 2 or J1979, the standard mandated many of the changes to the vehicles that you are repairing today. One of the many changes was to establish 5-digit trouble codes (DTC’s) (J2012) to enhance a technician’s ability to repair the vehicle. Each digit of your DTC indicated something specific about the fault that was present.

1st digit: P, C, B, U:
P = Powertrain,
C = Chassis,
B = Body,
U = Communication

2nd digit: 0, 1:
0 = Generic, which indicates the DTC meaning is the same for all vehicles.
1 indicates the DTC is manufacture specific.

3rd digit:
0 = Total system,
1 = Fuel system,
2 = Fuel and air metering system
3 = Ignition or misfire
4 = Auxiliary emissions
5 = Speed, idle, auxiliary inputs
6 = ECM and auxiliary inputs
7 = Transmission
8 = Transmission
9 = Transmission
A, B, C = Hybrid

4th and 5th digits:  Area or component that is involved.
As an example let’s look at a P0115 coolant temperature DTC:
P = Powertrain
0 = Generic
1 = System
15 = Coolant temperature sensor/circuit

The move to 5-digit DTCs made the technicians job easier but it still left a lot to the imagination when it came to the exact type of failure that was causing the DTC.

In 2013, SAE developed new enhanced DTC standards for J2012 (ISO 15031-6). The J2012 standard now requires the manufacturers to display the DTC in a seven-digit format. The extra digits are used as “symptom identifiers” to describe to the technician what the cause of the DTC is. This new standard dramatically shortens the amount of time for diagnosis of the DTC as it helps to pin point the cause; (i.e. short to ground versus a short to voltage as an example).

Looking at the same example as earlier, a coolant temperature DTC, we can see how this would work.

As an example, let’s look at a P011511 DTC:
P = Powertrain
0 = Generic
1 = System
15 = Coolant temperature sensor/circuit
11 = Short to ground

The last 2 digits really help you isolate the issue which ultimately reduces misdiagnosis of the cause as well as reduces the time it takes to diagnose the concern.

The list of the symptom identifiers is quite long, listed below are just some of the identifiers available.
00 = Not specified
04 = Open
11 = Short to ground
12 = Short to B+
13 = Open
14 = Short to ground or open
15 = Short to B+
16 = Circuit voltage below threshold
17 = Circuit voltage above threshold
18 = Current below threshold
31 = No signal
44 = Data memory failure
47 = Controller failure
49 = Internal electronic failure
51 = Not programed
62 = Signal comparison failure
64 = Plausibility failure
72 = Actuator stuck closed
74 = Actuator slipping
77 = Commanded position not achievable
7E = Actuator stuck on
1A = Circuit resistance below threshold
1C = Voltage out of range
1D = Current out of range
23 = Signal stuck low
24 = Signal stuck high
27 = Single rate of change above threshold
29 = Performance signal invalid
2A = Stuck in range
2B = Signal cross coupled
2F = Signal erratic
7F = Actuator stuck off
85 = Signal above allowable range
87 = Missing communication message
93 = Performance no operation
96 = Component internal failure
9C = Low insufficient flow
9E = Stuck on

As you can see, this feature is really a step in the right direction on the diagnostic front. The only downside to the new format is to make sure that your scan tool is capable of interpreting the 6th and 7th digits. Some scan tools have both a generic and an enhanced mode. The generic mode may not display the J2012 DTC format so you may need to choose the enhanced mode. Most manufactures started rolling out the new DTC format shortly after the standard was released. If your scan tool is not displaying the DTC in the enhanced format you really need to contact your scan tool manufacturer to find out where the function is located on your tool. If the scan tool manufacturer indicates that their tool is not currently capable of displaying the enhanced format, update the tool as soon as new software is available to address the issue.

Vehicle diagnosis is always a challenge so it is nice to see the OEM’s moving in the right direction. Until next time remember. “It does not matter how slowly you go as long as you don’t stop.