Description

1986 BMW 735i Troubleshooting Manual

If you have ever stared at a nest of corroded wires under the dash of a 1986 BMW 735i with no idea which circuit feeds the ABS module or why the SRS light won’t clear, you know the value of a factory Troubleshooting Manual. Aftermarket wiring diagrams are worthless – they leave out splice locations, connector pinouts, and the exact logic the control units use. This 174-page OEM manual gives you the same book the dealer techs had in 1986. No shortcuts.

Your time matters. So does your safety. Every section in this manual was written by engineers who built the car. You get the charging system, starting circuit, engine control block diagrams, and the full injection electronics layout. Need to trace a no-start condition? Page 6 starts the systematic troubleshooting procedure – follow it step by step and you will not replace parts that are fine.

1986 BMW 735i Troubleshooting Manual: What’s Covered

The table of contents reads like a parts list for every electrical system on the car. Power distribution (0670), charging system (1230), start circuit (1240), engine control block diagrams (1250), injection electronics (1360), electronic transmission control (2460), supplemental restraint system (SRS – 3234), brake lining warning (3435), antilock braking system (ABS – 3450), power mirrors, central locking, power windows, seats, sunroof, and the full body electrical section (6100). Every fuse, relay, and splice is shown with factory part numbers. If you can’t find the right diagram in an aftermarket book, it’s because they cut corners. This manual does not cut corners.

Systematic Troubleshooting on Page 6

Page 3 explains how to use the manual – read it before you touch anything. Then turn to page 6. That’s where the step-by-step diagnostic logic starts. You are supposed to check power at the fuse box before you order a new control unit. Too many guys skip that step and end up with a $400 ECU that still doesn’t work. The systematic approach forces you to verify voltage drops, ground continuity, and signal paths in the right order. It’s boring but it works.

Why You Need an OEM Wiring Diagram

Every wire gauge, color code, and connector shape is documented with views starting at section 8500. Aftermarket manuals guess the colors. BMW printed these diagrams from the master engineering files. When the diagram says pin 3 on the ABS hydraulic unit goes to the left front wheel speed sensor, you can bet your test light it’s correct. The [Automotive Industry Overview] standards demand that level of accuracy. This manual meets them. If you are swapping in a manual transmission from another chassis, the transmission control section won’t apply, but you can use the [Manual Transmission] general info as a reference.

Get the Right Diagnostic Procedure for ABS

Section 3450 covers the antilock braking system. You get the full schematic, component location views (7000), splice location views (8000), and a component location chart (9000). The ABS computer has a self-diagnostic mode – the manual tells you how to read blink codes without a scan tool. Brake lining warning (3435) is separate – do not confuse the two. Ignoring the correct procedure will put a customer (or yourself) into a wall.

SRS and Airbag Systems: Factory Specs

Section 3234 covers the Supplemental Restraint System. This is not a system to guess on. The manual includes specific resistance checks and connector handling instructions. You will find the power distribution box fuse data (0670-1) referenced in the SRS section. If you disconnect the battery without waiting the specified time, the airbag can deploy while you are working. The 1986 735i Troubleshooting Manual warns you about that on the relevant pages. Take the warning seriously.

That is the difference between a repair and a mess.

Charging, Starting, and Engine Control Block Diagrams

The charging system (1230) and start circuit (1240) are laid out so you can test the alternator excitation wire and the starter solenoid circuit without removing anything you don’t need to. The engine control block diagrams (1250) show the relationship between the Motronic unit, the injection electronics (1360), and the sensors. If you have a hesitation or rough idle, start with those sections before you throw parts at it.

For later model years, check the [BMW 7 Series 1988-1994 Service Manual] for mechanical procedures. If you need a similar electrical manual for the 1988 model, the [BMW 735i 1988 Electrical Troubleshooting Manual] is available. And for the V12 models, see the [BMW 735i 735iL 750iL 1990 Electrical Troubleshooting Manual].

Will this manual work for a 1987 735i?

Yes. The manual covers both 1986 and 1987 model years as stated on page 3.

My car has a different options list – will the wiring still match?

This manual includes multiple wiring variants for optional equipment like cruise control, active check control, on-board computer, and memory seats. The component location chart (section 9000) lists each option code. You need to cross-reference your car’s option codes against the diagrams. It takes time, but every wire is accounted for. If your car has a dealer-installed accessory that was never in the factory books, you are on your own. For everything else, this manual is the final word.

Stop burning through test lights and guessing which relay is which. Access the factory manual and get the wiring right the first time.