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Fuel Injection DME Relay Testing
 
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Pelican Technical Article:

Fuel Injection DME Relay Testing

Nick Czerula

Time:

1.5 hours

Tab:

$50

Talent:

*****

Tools:

Multi-meter, test light

Applicable Models:

BMW Z3 (1996-02)

Parts Required:

DME relay

Hot Tip:

Check fuses before digging too deep

Performance Gain:

Properly functioning engine control system

Complementary Modification:

Replace unloader relay

BMW Z3 sports cars (1996 - 2002) are equipped with digital engine management systems (called Digital Motor Electronics or DME). The engine control module (ECM) in these systems is programmed with software for control of fuel injection, ignition and other functions. BMW DME systems comply with second-generation on-board diagnostics (OBD II) standards.

The DME main relay, the primary power source for nearly all engine management functions, supplies battery power to the engine ECM when the ignition is activated. A faulty DME relay can cause poor engine performance and hard starting problems. When it fails completely you may be left with an engine that doesn't start. If your DME is not activating, the engine is not starting and the check engine light does not illuminate when the key is ON, you will have to determine if the issue is a power supply problem or something else. This article will help you test the DME relay, the power source for the DME. Before condemning the ECM, always check power and ground. 

The DME main relay is located in the right side (passenger side) E-box. There is a black box next to the jump start terminal that houses the DME and Unloader relay. The vehicle used in this tech article was a 1998 Z3 with a 4-cylinder engine. The DME relay position varies slightly depending on year, and it moves its position inside the relay box. Double check your DME relay location with the latest BMW repair information.

To avoid marring the paint and trim, work with a plastic prying tool or wrap a screwdriver tip with masking tape before prying out body or interior items.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches. 

When performing electrical tests, be sure to use a digital instrument such as DVOM. Using an analog device may lead to damage to sensitive electronic components.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability. 

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Press the relay cover release tab (green arrow) to remove cover.
Figure 1

Press the relay cover release tab (green arrow) to remove cover.

The DME relay (green arrow) and the Unloader relay (yellow arrow) are both located in the relay box, next to the DME.
Figure 2

The DME relay (green arrow) and the Unloader relay (yellow arrow) are both located in the relay box, next to the DME.

If you suspect your DME relay is faulty, the quickest test (for the relay itself) is to remove it and swap it with a relay of the same color.
Figure 3

If you suspect your DME relay is faulty, the quickest test (for the relay itself) is to remove it and swap it with a relay of the same color. To remove the relay, pull it straight up out of the electrical connector. Swap a relay of the same color into the slot, check if you now have DME function. If you do, the relay is likely faulty. If swapping the relay does not help, continue to test the circuit.

With the relay removed, you can identify the terminals and functions.
Figure 4

With the relay removed, you can identify the terminals and functions. Terminal 86 (green arrow) is the positive side of the low current switch. This should have battery positive volts with the Key ON. Terminal 30 (red arrow) is constant power to the relay. This should have battery positive volts all the time. Terminal 85 (blue arrow) is the battery negative side of the low current switch. This should be close to zero volts with the key ON. Terminal 87 (yellow arrow) is the battery positive output to the DME.

I like to remove the electrical connector from the E-box, then reconnect the relay.
Figure 5

I like to remove the electrical connector from the E-box, then reconnect the relay. This allows me to test the wires at the bottom of the relay while it's plugged in. Press the release tab (yellow arrow) and pull it up to remove.

Install the relay, then using the earlier identified terminals, you can test relay function at the bottom, at the wires.
Figure 6

Install the relay, then using the earlier identified terminals, you can test relay function at the bottom, at the wires. In the next few steps, I will use my DVOM (Digital Volt-OHM Meter) and test light to check each terminal (with the relay removed). You will see expected values on a working vehicle. If you choose to test the relay while it is installed, use the specifications listed below:
Terminal 30 - constant battery positive
Terminal 86: switched battery positive, present when key is in ON position
Terminal 85: DME relay control, close to zero volts when DME turns relay on
Terminal 87 - Feed to DME, battery positive when relay is activated

With the relay removed, let's review what you should see and where.
Figure 7

With the relay removed, let's review what you should see and where. Terminal 30 - constant battery positive. I suggest load testing using a test light and a DVOM. Connect the DVOM positive lead to terminal 30 and take a reading, it should read battery volts all the time. Then connect an incandescent bulb style test light to battery ground and touch the test light probe tip to the positive wire you are backprobing with DVOM. Your reading should hold steady, a maximum drop in voltage of 0.5 volts is OK. Anything more is a problem. In this photo, voltage held steady. Note the voltage is high due to a battery charger being connected to the subject vehicle.

Terminal 86 - battery positive.
Figure 8

Terminal 86 - battery positive. I suggest load testing using a test light and a DVOM. Connect DVOM positive lead to terminal 86 and take a reading. It should read battery volts all the time. Then connect an incandescent bulb style test light to battery ground and touch the test light probe tip the positive wire you are backprobing with DVOM. Your reading should hold steady, a maximum drop in voltage of 0.5 volts is OK. Anything more is a problem. In this photo, voltage head steady.

Terminal 85: relay coil control.
Figure 9

Terminal 85: relay coil control. I suggest load testing using a test light and a DVOM. Connect the DVOM positive lead to terminal 85 and take a reading. It should read battery negative volts all the time. Then connect an incandescent bulb style test light to battery positive and touch the test light probe tip to the positive wire you are backprobing with DVOM. Your reading should hold steady, a maximum drop in voltage of 1.0 volts is OK. Anything more is a problem. In this photo, voltage dropped 0.2 volts.

You can also jump out your DME relay (to bypass it) for testing.
Figure 10

You can also jump out your DME relay (to bypass it) for testing. Connect a fused jumper wire between terminals indicated by arrows. The green arrow points to terminal 30 (battery positive). The yellow arrow point to terminal 87 (DME positive feed). Keep in mind, it is the too larger wires you are jumping. This will also activate your DME. Battery volts should be present. Terminals may vary so double check your model against a wiring diagram.











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Comments and Suggestions:
Bill Comments: Which DME system is used on a 1998 Z3 1.9l engine?
January 8, 2016
  Followup from the Pelican Staff: That info is here:

http://www.pelicanparts.com/BMW/techarticles/BMW-Z3/58-FUEL-Engine_Management_Systems/58-FUEL-Engine_Management_Systems.htm - Nick at Pelican Parts
 
bzsm Comments: Thanks Nick! I did have have the intake crossed with the return. Made the switch and she runs like a charm agajn. Won't make that mistake again.
July 19, 2015
  Followup from the Pelican Staff: Cool. Glad to help and thanks for the follow up. - Nick at Pelican Parts  
Steve Comments: Thanks for the response. The filter has two intake ports. Does it matter which feed line goes into which port?
July 15, 2015
  Followup from the Pelican Staff: Yes, it does matter, as one is a return. - Nick at Pelican Parts  
bzsm Comments: Hi, I have a 2001 Z3 with an M54 engine. I changed my fuel filter yesterday. To relieve the pressure in the lines, I started the engine and removed the #13 fuel pump fuse. The engine stopped within a few seconds. I changed the filter and and connecting hoses including the vacuum hose, which was a straightforward procedure. Now the engine cranks, but wont start. Before I changed the filter, it always started immediately. Could I have burnt out the DME or the relay? I am not too much of an electrical buff, I lean more to the mechanical side. I will try your test procedures, but have you heard of my problem happening with a simple filter change? What else might it be? Any suggestion would be GREATlY appreciated! Thank you. Steve
July 12, 2015
  Followup from the Pelican Staff: Nothing can be burnt out by removing the fuse. Check if the fuse is installed in the correct place. Also check if fule filter is installed in correct direction, arrow facing forward. - Nick at Pelican Parts  

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Page last updated: Wed 12/7/2016 02:38:27 AM