Let me first explain the DTC.
The error code is made up of 5 characters.
The 1st character identifies the system related to the trouble:
P = Powertrain
B = Body
C = Chassis
U = Undefined
The 2nd character defines whether the code is generic or Manufacturer Specific:
0 = Generic
1 = Manufacturer Specific
The 3rd character indicates the type of sub-system that the error pertains to:
1 = Emission Management (Fuel or Air)
2 = Injector Circuit (Fuel or Air)
3 = Ignition System or Misfire
4 = Auxiliary Emissions Controls
5 = Vehicle Speed and Idle Control System
6 = Computer Output Circuit
7 = Transmission (gearbox)
8 = Transmission
9 = SAE Reserved
0 = SAE Reserved
A, B, C = Exclusive for Hybrid Propulsion
The 4th and 5th characters relate to a particular problem:
Fault (00 – 99)
Let’s look at a common reading such as P1128 and or P1130.
If you’re using the cheapest code reader, probably that’s all you’ll see: P1128.
You would then have to refer to a list of codes to look up the meaning of the code.
If it’s a generic code, it will probably be included in the list, but if it’s a Porsche-specific code, you’re on your own.
But using the above information you can now start to decipher it:
P = Powertrain issue
1 = Porsche Specific
1 = Emission Management Sub System
28 = Particular Problem
The more expensive code readers apply this knowledge and offer additional information from its memory:
P1128: Oxygen Sensing Adaptation, Range 2 (cylinder 1-3) Enrichment limit
P1130: Oxygen Sensing Adaptation, Range 2 (cylinder 4-6) Enrichment limit
So, what does it really mean?
It means that the fuel/air mixture is so lean that the control is up to the enrichment limit.
Most people who get these error messages and want to fix the issue themselves see “Oxygen Sensing” and immediately assume that the oxygen sensors are bad and need to be replaced, so they go and purchase 4 sensors, replace them, clear the codes and a few miles later the CEL comes back on and the same two error codes appear.
You really have to look deeper in order to figure out what’s going on.
The bottom line is that the DME is sensing that the mixture is too lean, which means that there is more oxygen in the mixture than there should be.
What could cause those readings?
1.- The O2 Sensor could be bad and reads a higher amount of oxygen than actual
2.- There could be an air leak after the Mass Airflow Sensor (MAF)
3.- The MAF could be bad (or dirty) and is reading less air going through it than actual
4.- There is less fuel getting to the cylinders due to:
a) Low fuel pressure in the system because of a bad pump or clogged fuel filter
b) Fuel supply too low (due to above)
c) Clogged (carbonized) fuel injectors which don’t allow enough fuel through them
Now is when experience and knowledge kicks in. An experienced tech will check the most logical issue first:
An air leak after the MAF probably due to a loose hose clamp.
If not, then move to: dirty MAF and so on.
Last on the list are the oxygen sensors which in my opinion are almost bullet proof. In my car, they are the original sensors and are still reading fine. BTW they have been working now for over 280,000 miles!
Bedsides, it is very rare when all the sensors fail at once. It’s usually one bank or the other, not both at once.
Most people want to DIY and save some money, but many times they end up spending more in parts than necessary. If you must DIY, arm yourself with knowledge from people who share it with you (not just from the Internet) and know when to say UNCLE!
Published in the September 2017 issue of “Die Porsche Kassette”
Ⓒ2017 Technolab / PedrosGarage.com
For more information on DTCs, Porsches and more, please visit my website:
During WW-II the Germans encrypted their secret messages using the “Enigma” Machine so that even if the messages were intercepted, they couldn’t be understood by the Allies.
Similar to the DTCs (Diagnostic Trouble Codes) in your car, right?
The DTCs are error codes stored in your Porsche’s diagnostic system’s memory which are very misunderstood by the general public but which can be deciphered not with an Enigma Machine, but with a scan tool, knowledge and experience in these cars.
All cars since 1996 have the standardized OBD-II (On-Board Diagnostic - II) which monitors the many systems in your Porsche which affect, among others, the Airbag Light, the ABS Light and the infamous Check Engine Light.
These DTCs can be read using anything from an inexpensive Scan Tool (Code Reader), to the very exclusive factory tool known as the PIWIS (Porsche Integrated Workshop Information System). You simply plug it into the OBD-II port in your car and read the code. And that’s when the fun begins.