BMW models with Turbocharged N54 engines and MSD80 DME Software can develop fuel injector MOSFET driver failure. This will cause an injector to stop delivering fuel and an engine misfire to occur. The check engine light will be ON with the related Fault Codes (error messages):
- 30BA DME digital motor electronics, internal failure
- 30BB DME digital motor electronics, internal failure
This article and video shows you how to diagnose these fault codes and test the signal from the DME to the fuel injectors. You will also see how to isolate and test each wire for the fuel injectors and test the DME MOSFET Drivers.
- 2007-2013 BMW 135i (E82)
- 2007-2008 BMW 335i (E90)
- 2007-2008 BMW 335xi (E91)
- 2007-2010 BMW 335i (E92)
- 2007-2010 BMW 335i (E93)
- 2009-2010 BMW 535i & 535xi (E60)
- 2009-2016 BMW Z4 35i (E89)
BMW models with MSD80 DME software may set the fault codes 30BA or 30BB. These fault codes set when fuel injectors on bank 1 or bank 2 develop circuit faults or an injector MOSFET driver fails. Most times these fault codes will be permanent and will not clear. However there are situations where the fault codes will set intermittently. Keep that in mind when diagnosing.
When diagnosing Piezo fuel injector fault codes it is a good idea to begin by checking fuel injector voltage and current using a scope. This can help to narrow down the cause of the fault code, the injector, circuit or DME injector driver.
Begin by removing the cabin microfilter housing and engine covers.
Locate the injector wiring harness for the fuel injector you want to test. Our subject vehicle has a code for injectors 4 5, 6. Before testing injectors 4, 5 and 6, we will start by checking the signal at injector 2 to confirm a possible good pattern.
WARNING HIGH VOLTAGE
Piezo injectors normally operate at voltages up to 200 volts. Extreme care should be taken to protect against shock. Do not touch any of the injector terminals while the engine is running.
Set your scope to display voltage and current at the same time. Set the voltage range to -200 volts dc to +200 volts dc. Our current range is set to -10 amps to + 10 amps. Current ranges will vary depending on your probe and scope. Set it accordingly to display 10 amps.
Start engine and allow it to idle, be sure the exhaust is properly vented.
Beginning on injector 2, to establish a possible known good pattern, insert a backprobe into the white wire, then attach your current probe around the same wire. Confirm connection points using a wiring diagram for the vehicle you are working on.
The pattern shown is a good injector and DME mosfet driver. Voltage should range from 0 to almost 160 volts dc.
The current pattern will peak around 8 amps when the injector is switched on, current will drop while injector is open, then reverse when the injector is switched off. Current reverses because the Piezo element acts as a capacitor, and when switched off, the voltage travels back through the injector.
Next we connect to injector 4. The scope pattern shown is a bad injector or DME. Most times when the DME is at fault, the current pattern will try to climb, but fail. The MOSFET drivers fails when the attempt to charge the injector begins.
Turn the engine off and cycle the key, remove the key from the vehicle. Disconnect all fuel injector electrical connectors.
Turn the key on with the engine off. Using your AssistPlus device, clear DME fault codes. If the fault code will not clear, the issue is most likely in the injector wiring or DME.
On our subject vehicle the fault code will not clear. Leave fuel injectors disconnected.
Disconnect the negative battery terminal.
Working on the right side of the engine compartment at the E-box, Pull up on the E-box locking tabs and slide both locking fasteners. Remove the E-box cover.
Disconnect both DME electrical connectors by sliding the lock away from the connector while lifting connector off DME.
Find a suitable wiring diagram for the DME. Check the integrity of each wire from the DME to each fuel injector. Make sure to also verify each pin has good pin tension. The best way to check wire integrity is to voltage drop test the wire under load.
With our meter set to Ohms, insert the positive test lead into the injector wire to be tested.
Then use the negative lead to confirm the location of the terminal at the DME. Be sure to use specialized test adapters as to prevent damage to the DME terminals.
With the wire to be tested identified, connect the injector side of the wiring harness to battery negative. Then at the DME connect an incandescent test light (our load) to the injector terminal to be tested, then connect it to battery positive. In this case we are connecting at the jump start positive terminal. The test light should illuminate.
Next, check battery voltage at the jump start terminal, we have 12.44 volts dc.
Then check the voltage DME connection, this reading will be your voltage drop. We have 0.11 volts dc, this is a good reading. This confirms that injector wire to the DME is good. Repeat this test for each leg of each injector, two wires per injector.
Since the fault code 30BB does not clear even when disconnecting all the injectors and the injector wiring tests OK, the issue has been isolated to the DME.
Place an anti static mat on your work surface. Next remove the DME from the E-Box and place it on the anti static mat.
Wear an anti static wrist band.
Using a flatblade screwdriver, pry away all the metal tabs on the DME cover to remove it. There is a total os six tabs around the DME housing.
On the right side of the circuit board, you will find 6 MOSFET drivers. These are responsible for fuel injection activation.Each injector has a single MOSFET (transistor) driver. MOSFET drivers are used due to the low input current needed to control each injector.
Set your DVOM to check resistance, or Ohms. Connect the negative lead of your DVOM to the drain. Then connect the red lead of your DVOM to the gate and source. The DVOM should show no continuity and shouldn't beep.
On our subject vehicle, the MOSFET will have continuity between the drain and source all the time. Our subject vehicle has a faulty mosfet at injector 4.
DME replacement is needed if a MOSFET is found to be faulty.
Need help diagnosing this or any other fault on any make or model vehicle? Get in touch with an Autologic Technical Support Specialist.