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Reading Fuel Injection Fault Codes / Diagnosing Problems
 
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Pelican Technical Article:

Reading Fuel Injection Fault Codes / Diagnosing Problems

Time:

30 min

Tab:

$300

Talent:

*

Tools:

Durametric Software

Applicable Models:

Porsche 986 Boxster (1997-04)
Porsche 986 Boxster S (2000-04)
Porsche 987 Boxster (2005-08)
Porsche 987 Boxster S (2005-08)

Parts Required:

-

Hot Tip:

The Durametric software is essential to diagnosing problems

Performance Gain:

Better running engine when the problems are fixed

Complementary Modification:

Replace O2 sensor " the computer often shows this error code
101 Performance Projects for Your Porsche Boxster

This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster. The book contains 312 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 950+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website for more details.

Almost all Porsches from about 1984 use a sophisticated Bosch engine management system called Motronic. The Motronic system (also called the Digital Motor Electronics or DME) is hands down the best overall fuel injection system that you can use when you consider price and performance. Ignition timing and fuel delivery are all controlled by a digital map that is recorded in a removable chip within the main fuel injection (DME) computer. The computer takes input from a variety of sensors that are located on the engine: engine coolant temperature, crank angle, throttle position, exhaust gas oxygen (mixture), ambient air temperature, and mass air flow. The DME flash memory chip is programmed from the factory with certain performance characteristics (mostly conservative) so that the engine will react well under a host of varying conditions.

As with any electronic device, components can fail, triggering problems with the system. The Porsche Motronic system is designed to react to these failures and indicate them to the driver, so that they can be fixed. If one of the computer's sensors is not working properly, then the computer may not be able to successfully identify the current state of the engine and choose the appropriate fuel mixture or timing advance level. When this happens, the fuel mileage drops, engine performance suffers, emissions increase, and the car typically illuminates the 'check engine' light.

Pre-1995 Porsches were equipped with what is known as OBD I (On Board Diagnostics Level I). Starting in 1996, they were equipped with a more advanced version called OBD II, which was mandated by the US government, in order to standardize automotive repair and diagnostics. The OBD system is responsible for monitoring and checking all of the fuel injection sensors and systems in the vehicle, and turns on the 'check engine' lamp if it finds a problem or irregularity with one of them. If there is a problem with a sensor or component, the computer lodges a Diagnostic Trouble Code (DTC) in the main computer until it is read and reset.

In order to accurately find the sensor and fix the problem, you will need to find out which error code is being triggered by the computer. There is no method to pull these codes out of your Porsche without the use of a computer tool. The factory has produced a version of this tool for use by Porsche dealers, called the Porsche System Tester 2. Unfortunately, finding one of these is next to impossible, and they cost about $4000 used anyways. There's a newer version of the PST2 called the PIWIS, but getting your hands on one of those costs about $20,000 and a $1,000 maintenance contract from Porsche. You can indeed use a standard off-the-shelf OBD II reader available at any auto parts store, but it will only give you the standard read-out codes for the fuel injection system: you will not be able to do any extra diagnostics on any other area of the car.

Thankfully though, there is aftermarket software available produced by Durametric that performs almost all of important reading functions that the PST2 does. It runs on a windows laptop computer and the cost is about $300 for the home-based version that will allow you to read codes on up to three cars. If you're planning on working on your Boxster at all, I suggest that you pick up this essential tool.

With a standard ODB II code reader, you can access and reset the codes on the car that are related only to the fuel injection system. The PST2 and Durametric software allow you to dig deep into the various systems of the car and read values from the various systems of the car (airbag, ABS, Tiptronic transmission, alarm, seat memory, heating & A/C). The Durametric tool does not program the computer though: you are still at the mercy of the dealer when it comes to making changes to any of the non-fuel injection settings on your car.

When you obtain the trouble codes output by the PST2, you can look them up in the Porsche ODB II factory diagnostic book (expensive), or refer to the Bentley Workshop Manual for additional details. Both manuals have extensive sections describing the various faults and what is needed to fix them.

Tip: Wire harnesses are a major cause of fault code problems. As the cars get older, the wiring harnesses have a habit of becoming what is commonly known as 'work hardened.' This causes the wiring to become brittle and often break inside of its plastic sheath. Only by testing the continuity of the wires end-for-end will you be able to determine whether the wire is broken or not.

Here it is, the holy grail of Porsche code reading.
Figure 1

Here it is, the holy grail of Porsche code reading. The Porsche System Tester 2 (PST2) is a rare and expensive tool that can be used to diagnose multiple car systems on a variety of Porsches. Every dealer has one of these, or the later-model PIWIS tester so that they can quickly diagnose problems and change settings on the various computer systems within the car.

Both the PST2 and the Durametric software interface with the car through the OBDII port located beneath the steering wheel on the lower left hand side of the car.
Figure 2

Both the PST2 and the Durametric software interface with the car through the OBDII port located beneath the steering wheel on the lower left hand side of the car. Make sure that the plug is firmly seated as it has a tendency to occasionally fall out.

Shown here is a screenshot of the Durametric software available for diagnosing various system problems.
Figure 3

Shown here is a screenshot of the Durametric software available for diagnosing various system problems. The software is nearly as powerful as the reading functions on the original Porsche PST2 and is a required diagnostic tool for the do-it-yourself enthusiast.

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Comments and Suggestions:
Ricky Sanchez Comments: Can a bad AOS in a Porshe Boxster 986 result in acceleration problems? We found oil in the ventilating tube and also there is suction in the oil cap, meaning a bad AOS. We assume that it is creating a negative suction in the intake manifold that results in a lean mixture while accelerating creating hesitation and POP POPs when accelerating. If we spray starting fluid directly while accelerating it works perfect. There are no codes.
September 6, 2016
  Followup from the Pelican Staff: If popping you have either a large vacuum leak or a timing issue. If the AOS diaphragm has failed, it could be your issue. Fuel trim numbers should show this, skewed with a correction for a lean condition. - Nick at Pelican Parts  
Michael Comments: So, I last weekend I cleaned the MAF, the throttle body and intake plenum and replaced the AOS. The car runs great now and no more smoke. I drove it for two days and the CEL came on last night. The P1130 code is no more but now I just get the P1128 error, could it be a bad oxygen sensor or something else?
August 31, 2016
  Followup from the Pelican Staff: I would assume the mass air flow sensor was damaged when cleaning it. Hot film style MAF sensors should not be cleaned. - Nick at Pelican Parts  
Nismou20 Comments: After modding my 02 -S with 996 TB, 997 -T and 987 airbox, I have been throwing the infamous P1128,1130. I have double, triple checked for air leaks, and cleaned the MAF. I'm wondering if I need a higher fuel pressure regulator due to better breathing with mods.do you suppose a 996 FPR is called for over my oem 986 regulator?
August 22, 2016
  Followup from the Pelican Staff: You will need software likely, the regulator won't fix fuel delivery mapping. - Nick at Pelican Parts  
Michael Comments: The fault codes are P1128 and P1130, see the attached image. Thank you!!!
August 20, 2016
  Followup from the Pelican Staff: These are fuel trim faults, supporting your suspicion of the AOS. - Nick at Pelican Parts  
Michael Comments: Two updates, looks like I actually do have the Porsche Enhanced Interface Expansion but the mechanic cleared the fault codes so now I have to wait for the next CEL to determine the issue. I was convinced it was the AOS since the car is smoking but he was unable to get it to.
August 18, 2016
  Followup from the Pelican Staff: With smoke, it could be the AOS. You can check crankcase pressure with a test kit and adapter. Or replace it and see if the fault returns. - Nick at Pelican Parts  
Michael Comments: It's a 2001 Boxster not an S. I will have to get the fault code later today.
August 18, 2016
  Followup from the Pelican Staff: Thanks. - Nick at Pelican Parts  
Michael Comments: I have the AutoEnginuity ScanTool but not the Porsche Enhanced Interface Expansion. I have a CEL and am not able to pass smog and my local mechanic hasn't been able to figure out what's wrong. Should I buy the Porsche Enhanced Interface Expansion or buy the Durametric kit?
August 17, 2016
  Followup from the Pelican Staff: Not sure. What is the fault code? What vehicle are you working on? - Nick at Pelican Parts  
LE Comments: I have a 02 Boxter coding po446. After fueling up in have to press the gas pedal to the floor in order to start the car. Also periodically idle fluctuatescrow from 3000 to 7000 rpms. I was told that it could be the evap canister valve. ???
February 18, 2016
  Followup from the Pelican Staff: The canister purge solenoid may be stuck open. - Nick at Pelican Parts  
8gokartracer Comments: I have a 1997 Boxster with P0123 and P1125 codes Engine Runs smooth at Idle but after car is slightly warm and when trying to move car doesn't have enough power to move engine will stall unless I push in clutch. Still Idles fine. Suspect Throttle sensor?
January 25, 2016
  Followup from the Pelican Staff: You have a fuel trim fault. That is an indicator of what you feel with the hesitation. Start by checking fuel control using a Porsche scan tool. Identify when the fuel trim is skewed. Then check parts depending on if vehicle is rich or lean and when.- Nick at Pelican Parts  
Obiwan Comments: I have a 2007 Boxster. The CEL comes on often. It produces a p456 code
which is usually the gas cap. I have replaced the gas months ago and the light still comes on frequently. Does anyone know of another solution to the
Annoying CEL. I have a feeling it has something to do with a valve/ flap on the gas tank refill neck,
November 16, 2015
  Followup from the Pelican Staff: This could be a faulty solenoid or hose. When the system is tested for evap leaks, a small one in present. I suggest smoke testing the system - Nick at Pelican Parts  
Joseph Comments: Hello I have a 97 Boxster and the dreaded CEL came on. The codes I got were P1124 and P1126, do you have any ideas on the fix?
August 2, 2015
  Followup from the Pelican Staff: These are fuel trim fault codes. Depending on when the codes were set, it could be a vacuum leak or the mass air flow sensor. Since both banks set faults, look for something affecting the entire engine. - Nick at Pelican Parts  
Sgtmaj Comments: My check engine light just came on and the P-codes showing up are P1124 fuel pump relay output stage and P1126 Oxygen sensing adaptation, lower load range cyl. 1-3. What do I need to do to correct this? 1997 Boxster. Thanks in advance
July 29, 2015
  Followup from the Pelican Staff: These are fuel trim fault codes. Depending on when the codes were set, it could be a vacuum leak or the mass air flow sensor. Since both banks set faults, look for something affecting the entire engine. - Nick at Pelican Parts  
Chris Comments: Hi, the engine check light recently came on and after connecting the OBD II reader it reported misfires on cyliders 4,5 & 6 P0300,P0304/5/6. Am about the check the plugs & coils and clean the MAF before replacing if needed although I didn't get any MAF specfic errors. Could it be anything else if these are the only codes? Thought about the o2 sensors but no codes to suggest this. Symptoms are stable at idle but if I press the throttle hard in neutral from idle it nearly stalls and takes a few seconds to recover back to a stable idle. Increasing revs slowly is OK. Just picked up the 101 projects book, it's brilliant - thanks!
May 1, 2015
  Followup from the Pelican Staff: A misfire can be caused by any part of the combustion process being faulty. I would check spark, fuel and compression on all cylinders. - Nick at Pelican Parts  
marty2900 Comments: having fault codes p1138 and p1130 ,I have replaced all the o2 sensors. reset cel ran a 100 miles had the codes come back up and had p1115 come up also. a little help ,direction . thanks marty
August 23, 2014
  Followup from the Pelican Staff: I would check the fuel trim using a Porsche scan tool. If it is skewed, it will set these codes. Once you see how it is skewed you will direction for your diagnosis. - Nick at Pelican Parts  
Ernie Comments: Your company has supplyed me with a new water pump and a new thermastat plus the gaskits, I put all the parts on myself and everything is just great I saved money not going to the dealer.I just used the Durametric soft wear with the cable you guys sold to turn off the airbag light, I am very happy with your service and all the things I have purchased from your company and if I shold need anything for my Boxster I will be calling on Yall again.
November 12, 2013
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help. - Nick at Pelican Parts  
Ernie Comments: I have orderd the Durametric software and the cable to reset the airbag code and to turn off that light so that I can get the car inspected, this tool do that wont it ?
November 1, 2013
  Followup from the Pelican Staff: I am pretty sure Durametric will do that. Check their site to see if it works with your model. http://www.durametric.com/default.aspx - Nick at Pelican Parts  

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