Introduction
This writeup is to explain how to make a remote starter trigger that plugs into the 20-pin diagnostic port. The point of the tool is to use the starter to turn over the engine, which make some jobs much easier (valve adjustment, compression test, leak-down test, etc.).
One of the shops I worked at had a super old tool that was incredibly useful for valve adjustments. I tried to find one for sale online, but it doesn’t seem like anyone makes them anymore. I could use a generic starter trigger, but then I’d need to reach down to connect to the starter. Making a plug-in tool is super cheap and easy, everyone should have one.
Theory
When you turn the key to crank the engine over, it triggers all sorts of systems to begin working (injection and ignition electronics). None of these are needed if you just want to get a cylinder to Top Dead Center (TDC) or to crank the engine for a compression test.
You can go to wedophones.com to find the Electrical Troubleshooting Manual (ETM) for your specific car. Some of the ETMs aren’t complete, so I tend to use the 1989 325i/325is manual as a guide for late model cars.
Sheet 8500-0 shows the pinout for the Diagnostic connector. Pin-11 is the Starter, Start Signal (50). Pin-14 is Battery (+).
Sheet 1240-0 shows the Automatic Transmission Start diagram and 1240-1 shows the Manual Transmission Start diagram. (The manual diagram is less complicated, so look at that one.) When you turn the key to Start, one of the things that happens is that 12 volts is applied to terminal 50 of the starter.
By connecting the diagnostic connector Pin-14 to Pin-11, you can trigger the starter without needing the key.
Parts
1) Solder
2) 1x Bosch FIX-7853 (available from Amazon for $15.11)
3) 1x Generic BMW 20-pin OBD-to-OBDII converter (available from Amazon for $9.99)
4) 2x TE Connectivity AMP 929975-1, Contact Socket 13-17AWG Crimp (available from Digi-Key or Mouser for $0.75/ea)
Tools
1) Prepare the 20-Pin Connector
- Use Philips Head screwdriver top unscrew the OBD converter (Part c)
- De-solder all connections
- Use solder wick to clean up pins
- Use small screwdriver to break seal between the OBD converter wire and the cable support
- Remove the cable support
2) Prepare the Starter Trigger (Part b)
- Cut off the alligator clips
- Slide the cable support onto the wires
- Strip about ¼ inch of wire
- Twist the wire tightly and tin the end with solder
- Use the crimp tool to crimp a connector (Part d) on each wire
- Flow solder into the crimped joint for extra durability
3) Assembly
- Tie the two wires together using a loose overhand knot. This will provide support against the cable support if someone pulls on the wire to remove the connector.
- Attach one connector to Pin-11 (starter trigger) and the other to Pin-14 (12 volt power)
- Solder the connectors onto the pins for extra durability
- Re-assemble the case
4) Test
- Plug it into the 20-pin port
- Make sure the car is in neutral with the parking brake applied.
- Squeeze the trigger and watch the starter turn over the car!
This writeup is to explain how to make a remote starter trigger that plugs into the 20-pin diagnostic port. The point of the tool is to use the starter to turn over the engine, which make some jobs much easier (valve adjustment, compression test, leak-down test, etc.).
One of the shops I worked at had a super old tool that was incredibly useful for valve adjustments. I tried to find one for sale online, but it doesn’t seem like anyone makes them anymore. I could use a generic starter trigger, but then I’d need to reach down to connect to the starter. Making a plug-in tool is super cheap and easy, everyone should have one.
Theory
When you turn the key to crank the engine over, it triggers all sorts of systems to begin working (injection and ignition electronics). None of these are needed if you just want to get a cylinder to Top Dead Center (TDC) or to crank the engine for a compression test.
You can go to wedophones.com to find the Electrical Troubleshooting Manual (ETM) for your specific car. Some of the ETMs aren’t complete, so I tend to use the 1989 325i/325is manual as a guide for late model cars.
Sheet 8500-0 shows the pinout for the Diagnostic connector. Pin-11 is the Starter, Start Signal (50). Pin-14 is Battery (+).
Sheet 1240-0 shows the Automatic Transmission Start diagram and 1240-1 shows the Manual Transmission Start diagram. (The manual diagram is less complicated, so look at that one.) When you turn the key to Start, one of the things that happens is that 12 volts is applied to terminal 50 of the starter.
By connecting the diagnostic connector Pin-14 to Pin-11, you can trigger the starter without needing the key.
Parts
1) Solder
2) 1x Bosch FIX-7853 (available from Amazon for $15.11)
3) 1x Generic BMW 20-pin OBD-to-OBDII converter (available from Amazon for $9.99)
4) 2x TE Connectivity AMP 929975-1, Contact Socket 13-17AWG Crimp (available from Digi-Key or Mouser for $0.75/ea)
Tools
- Soldering Iron
- Solder Wick (not critical)
- Wire Cutters
- Wire Strippers
- Crimping tool
- Philips Head Screwdriver
- Small screwdriver or pick tool
1) Prepare the 20-Pin Connector
- Use Philips Head screwdriver top unscrew the OBD converter (Part c)
- De-solder all connections
- Use solder wick to clean up pins
- Use small screwdriver to break seal between the OBD converter wire and the cable support
- Remove the cable support
2) Prepare the Starter Trigger (Part b)
- Cut off the alligator clips
- Slide the cable support onto the wires
- Strip about ¼ inch of wire
- Twist the wire tightly and tin the end with solder
- Use the crimp tool to crimp a connector (Part d) on each wire
- Flow solder into the crimped joint for extra durability
3) Assembly
- Tie the two wires together using a loose overhand knot. This will provide support against the cable support if someone pulls on the wire to remove the connector.
- Attach one connector to Pin-11 (starter trigger) and the other to Pin-14 (12 volt power)
- Solder the connectors onto the pins for extra durability
- Re-assemble the case
4) Test
- Plug it into the 20-pin port
- Make sure the car is in neutral with the parking brake applied.
- Squeeze the trigger and watch the starter turn over the car!
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