2005 BMW 325 P0171 P0174 227 228 Fault Codes Dinan Stage 2

The BMW had fault codes 227 and 228 stored (P0171, P0174) indicating a lean fuel system. This means the vehicle is running lean and the DME has tried to correct the condition but has reached it upper limit. Fault codes 227 and 228 are specific to a fault when the engine is at part throttle (not idle). This tells us that it’s unlikely the lean condition caused by and engine vaccum leak.


First I ran engine until it reached operating temperature. Then monitored fuel trim at idle using my scan tool. As you can see the Idle Load fuel trim is normal.

Next I went for a drive in the vehicle. I ran the engine through each RPM range from idle, steady cruise to WOT (wide open throttle). You can see the Part Load fuel trim is indicating a lean condition, (by adding fuel) during my entire test drive. Part Load does take some time to update, so I suggest a 15 minute test drive at the minimum.
During my test drive I am able to eliminate many possible causes of the lean condition. For example; I monitor Idle Load fuel trim at idle to see if it could be a vaccum leak. That coupled with freeze frame data ruleda vacuum leak out.
I also perform a WOT test on the fuel system. If the oxygen sensor holds above 800 mv for the entire time I am at WOT, the fuel pump and fuel delivery system can deliver enough fuel. Next I check the engine and exhaust system by looking at G/PS or Kg/H. This reading tells me about engine efficiency. I can estimate the amount of air at a given RPM, therefore testing the MAF sensor without touching it.

The 325 had Dinan performance software and an airbox, or what they refer to as Stage 2. I was convinced the problem was with the Dinan components but I have only an hour to prove this to be correct.

The airbox in modified by introducing a cold air intake, removing a baffle and changing the filter from a panel to a version of a cone style.

Here’s what I did.

I found the area where the baffle was removed (Dotted White Line) and temporarily mounted a piece of plastic in place.

I plugged the cold air intake port with a plastic cap.

Next I reprogrammed the car back to the factory DME software.

I went for a test drive, repeated the same RPM ranges as my previous one. The Part Load fule trim began to drop into an acceptable range.

Next I contacted Dinan with the information. They agreed to write a custom DME map for this car. Once I received the map I programmed the car again with Dinan’s MIP tool. It took a week or so to receive the new DME map, so the vehicle owner had to drive with the MIL light ON.

Once programmed I test drove the vehicle aagin, within the same RPM ranges. You can see part load came back down to a normal range and the vehicle is no longer exhibiting a lean condition.

This is a tricky fix. Without my standard fuel trim drive cycle test (to test components during the test drive), I may have replaced parts that were not faulty. It is important to approach each and every fuel trim fault the same way. A structured test plan will build confidence and make quick work of these common faults.

2001 Mercedes Benz C280 P1128 P1130 P2016 P2085 P2086

This was an easy fix – BUT I wanted to share how an aftermarket scan tool can improperly display Mercedes Benz fuel trim faults and values. We will look at it using a Snap On MODIS (same scanner software as all their models) using generic and Mercedes Specific software.

The following fault codes were stored.


Mercedes Specific

Scan data


Mercedes Specific

As you can see the values are flip flopped depending on which version of the scan tool I was using. What’s important is to check when the fault codes set and specific fault code definitions.
Additive or idle load will likely be vacuum leak.

Multiplicative or part load will likely be fuel delivery issues. ie. MAF, fuel pump.

Oh, you wanted to know the fix. After the MAF sensor mounted to the intake duct to throttle body there is a rubber hose. It is very common for this hose to crack and swell from oil contamination.

2000 Ford Windstar 3.8 P0171 P0174

Vehicle had fault codes for lean fuel system, both banks.

This indicates a problem affecting the entire engine.

With fuel trim faults, freeze frame data is a great starting point. Freeze frame data indicates fault codes set at idle.

Monitoring fuel trim during a test drive confirmed the vehicle was lean at idle. Note the graphs below indicate lean at idle. Once the engine RPM is raised from idle to 2500 rpm (in PARK) the fuel system is no longer lean. A vacuum leak can be detected this was. As the amount of unmetered air is larger (or comparable) compared to metered air. Once the RPM is raised the metered air amount becomes greater than the unmetered amount (vacuum leak).

After this I spoke to the mechanic who was working on the Windstar. He stated the same fault codes were present last month. He found a leaking intake manifold and a TSB. Therefore he replaced the front valve cover and intake manifold profile gaskets.


I quickly checked over his work. Everything looked in place. The only spot that propane could influence fuel control was at the intake manifold runner control bushing. I found this to be normal as all 3.8 intakes will have some level of leak here. New lower intake manifold does not remedy the leak.

I looked over the TSB and asked if he performed a needed PCM updated. They had not.

Next up I reprogrammed the PCM.

After the PCM software update I test drove the vehicle and confirmed it was now in proper fuel control. A second test drive confirmed the same result with no fault codes.

The shop was half way there. They performed almost all the needed repairs. A simple software update and they were done. With computers controlling almmost every function on late model vehicles it is always smart to check if software levels are up to date when performing repairs.

2004 BMW 330i E46 No start No Communication

2004 BMW 330i E46 No start No Communication

I received a call from a friend early in the week about a no start, no communication issue he was having. The offending vehicle was a 2004 BMW 330i. He stated the vehicle would start and run fine cold. Once it reached operating temperature, the temp gauge would go to hot and it would no start, (no crank condition). I informed him that when the instrument cluster loses comminucation to the DME the temp gauge defaults to full hot. As it gets it temperature information via the CAN-bus from the DME. Another good way to check if an ECM from almost any manufacturer is online is the MIL. In this case it was not.

The MIL is regulated to be on when the key is on and engine is off.


I pointed him in the correct direction and he was off to perform some tests. Once he got back to me everything was pointing at a faulty DME. Even though he is an experienced BMW mechanic he was second guessing himself. Asking me if I really thought he was on the right course. Reviewing his tests with me over and over again. He had that feeling in the pit of your stomach, the one you get right before you tell your boss the vehicle needs a $1000 part.. not including the labor to install or program.

Two days later my phone rang the caller ID showed it was the shop with the 330i. He had bad news, (as he put it).

I put in the new DME, it still won’t communicate with my scan tool and now it NEVER starts.

We spoke a few minutes more and I decided I had to get up there and look at the car myself. If you recall the original problem was the vehicle would start cold and stall once hot with no restart. Things are worse with the new DME.

The next night I drove north to Concord, NH to see what was going on with this 330i.

A short revealed the DME was now communicating. I always try with the factory scan tool, then with a generic OBD II scan tool.


One step further revealed a list of faults pointing to the DME.


When diagnosing bus faults it is important to identify the communication status of each module on the bus. A bus-system wiring diagram may be needed to verify all the modules involved.

The next step is to review fault codes stored, (if any) in each module. You want to write them down and see which module is being reported as not communicating by the most modules.

I now had my plan of attack and it was time to open up the diagnostic case. I hooked my pc-based scope. I am currently using the ATS limited. It is a small, powerful, 4 channel pc-based scope.


I gained access to the DME, which was easy as it was just replaced.


While attempting communication I would monitor the K-bus. The signal that was present was acceptable.


Moving to the CAN-bus next to confirm the signal there was acceptable. It was.


The CAN-bus does look quiet here. That is because during koeo all you will see is status messages. If the DME was online it would be much busier.

My tests confirm our earlier diagnosis via the telephone. I advised the shop to get another new DME. They were a bit worried because this was a new unit from BMW. I asked them to notify me when the new part would arrive.

I was back in the shop two days later, here is what I saw.

New DME installed, (not yet programmed).

Temperature gauge is is correct position. Indicating DME is online.


K-bus with DME online


CAN-bus with DME online. Much more traffic.


The second new DME fixed the problem.

1999 GMC Truck Erratic Speedometer – Shifting

5.7 liter engine 1999 GMC Cutaway.
The vehicle speedometer was erratic and the transmission would shift in and out of 2-3, 3-4 depending on speed. Very harsh shifts. No fault codes were stored in the PCM.

During a test drive I recorded scan tool data for review.
Let’s review the information in the graph:

  • Throttle (TP) angle looks normal.
  • Engine RPM looks normal
  • Input shaft speed (ISS) sensor looks normal.
  • Vehicle speed sensor (VSS) looks erratic
  • Output shaft speed (OSS) sensor looks erratic
  • VSS is generated from OSS sensor in the PCM. Knowing this I decided to scope the OSS sensor.

    Amplitude was all over the place. If it was tested using a DMM instead of a scope it would show up as ok, about 0.5 AC. Which is why a scope is superior in finding faults like this.

    What’s wrong with the pattern: The fluctuation of the zero point. if you look closely the amplitude changes each cycle. When I saw this I thought one thing, air gap had to be changing. Why else would voltage peak change during the same cycle?

    I pulled the driveshaft from the vehicle and installed a dial indicator.
    You can see the amount of movement in the shaft. The arrow indicates direction I am pressing.

    This proved my theory. The output shaft bushing was not good. There is a drum inside the transmission that the tone ring for the OSS sensor is welded to. The bushing for the drum was no good causing and air gap change between the sensor and the tone ring.
    I veryfied this by removing the OSS sensor and putting my finger into mounting hole. Once I could feel the tone ring for the sensor I moved the driveshaft back and forth. There should be little to no play and there was quite bit.
    The photo below shows locations of ISS and OSS (labeled as VSS).


    The transmission which was rebuilt within the past 30 days had to be disassembled and repaired again. The bushing was replaced and everything returned to normal.

    Ford Easy Fuel – No Fuel Filler Cap

    Ford’s Easy Fuel system uses an integrated spring-loaded flapper door to eliminate the need for a screw on fuel filler cap.


    •Easy Fue capless fuel-filler system has an integrated spring-loaded flapper door that allows customers to simply insert the fuel nozzle into the tank to fill up – no screw cap is required.
    •Easy Fuel automatically seals after the fuel nozzle is removed – no waiting for customers to re-secure the cap – emitting fewer evaporative emissions into the environment.
    •Easy Fuel was introduced on the 2008 Ford Explorer and Mercury Mountaineer, and will be offered as standard equipment on the all-new 2009 Ford F-150, Ford Flex and Lincoln MKS.
    •Ford will migrate Easy Fuel as standard across the Ford, Lincoln and Mercury passenger vehicle lineups during the next five years.

    The spring-loaded flapper door is held closed by two latches that can only be released by a standard-size unleaded fuel nozzle. When the proper nozzle is inserted into the filler neck of the system, the latches release, and the nozzle pushes the spring-loaded flapper door to the open position. When the nozzle is removed, the flapper door automatically is forced closed by the spring.


    The fuel filler pipe is then completely sealed, which prevents fuel vapors from escaping and helps reduce evaporative emissions.

    Every time a fuel cap is either lost or not screwed on properly hydrocarbon emissions enter the environment, with Easy Fuel, this is less of a problem.

    Easy Fuel also has a patented mis-fueling inhibitor to reduce improper fueling and siphoning. The inhibitor consists of a fuel nozzle detector that guides the nozzle to the opening. If a nozzle or foreign tube of a different size – a diesel nozzle or plastic hose, for example – is placed in the filler neck of a gasoline-powered vehicle, the latches will not release. For a diesel-powered vehicle, the inhibitor will keep out the smaller gasoline nozzles.

    To protect the fuel filler neck from dirt, dust and debris, Easy Fuel relies on a flexible rubber seal in the body housing. The system also comes with a handy plastic funnel, which is stored with a vehicle’s tire changing kit, in case someone runs out of fuel and needs to add a gallon or two from a portable container. The funnel is the same diameter as an unleaded fuel pump nozzle for a gasoline-powered vehicle.

    Diesel Emission DEF System Operation – 2010 EPA Regulation

    Diesel Exhaust Fluid (DEF), is a solution made from 67.5% purified water and 32.5 percent automotive-grade urea that serves as a carrying agent for the ammonia needed to reduce nitrogen oxide (NOx) emissions from diesel engines. When DEF is injected into the engine exhaust gas, downstream of the DPF, it will be rapidly hydrolyzed producing the oxidizing ammonia needed by the SCR catalyst to complete NOx emissions reductions. DEF begins to freeze at 12 degrees Fahrenheit (-11 degrees Celsius), manufacturers are incorporating a heating system to prevent this.

    Unlike other solutions used to control NOx, a DEF system allows the diesel engine to run at its optimum range in terms of fuel mixture – some systems require the engine to run richer, which can be harmful to diesel engines, to control the NOx.

    Selective Catalytic Reduction (SCR), is a general term for aftertreatment equipment which promotes a chemical reaction by using a catalyst for eliminating or detoxifying particular chemical ingredients. To meet the EPA2010 regulation, the vehicle out NOx level will be extremely close to zero (0.2 Grams per brake horsepower). By mixing the NOx with the ammonia contained in urea, it will be separated into harmless water and nitrogen. It is an extremely effective, dependable, efficient and economical selection. SCR has already been adopted in Europe and Japan for truck and mobile vehicle applications, so it only makes sense to be used as a solution for EPA 2010. Almost every U.S. diesel engine manufacturer plans to adopt SCR technology, further proving its reliability.

    How it works

    The first step in cleaning the diesel exhaust occurs when the exhaust stream enters the Diesel Oxidation Catalyst (DOC). The role of the DOC is twofold. First, it converts and oxidizes hydrocarbons –
    at about 250 degrees Celsius – into water and carbon dioxide.
    Second, the is used to provide and promote heat, using specific engine management strategies, into the exhaust system. Through appropriate thermal management, this heat increases the conversion efficiency of the downstream subsystem(s) in reducing emissions.

    The second step in the process is known as Selective Catalytic Reduction (SCR). In this process, the NOx in the exhaust stream is converted into water and inert nitrogen, which is present in the atmosphere and harmless. Before the exhaust gas enters the SCR chamber, it is dosed with Exhaust Fluid (DEF), also known as urea, an aqueous solution that is approximately 67.5 percent water and 32.5 percent pure urea.
    When heated, the DEF splits into ammonia and carbon dioxide. These molecules are atomized, broken up and vaporized, then enter a mixer that resembles a corkscrew. This twist mixer evenly distributes the ammonia within the exhaust flow. The ammonia enters the SCR module, which contains a catalyzed substrate, and through chemical reactions combines and converts the NOx and ammonia into the harmless inert nitrogen and water. Dosing typically occurs between 200 and 500 degrees Celsius.

    The final step of the cleansing system for the diesel exhaust gas involves the Particulate Filter (DPF). DPF traps any remaining soot, which is then periodically burned away, known as regenerating, when sensors detect the trap is full. The regeneration process sees temperatures in excess of 600 degrees Celsius to burn away soot.