E30 No-Crank / No-Start Guide

What does the car do when you turn the key to START?

Pick the closest match. You can go back at any point.

Check the battery and its connections first

A flat battery or a loose terminal causes more no-starts than anything else, and it can imitate almost every other fault.

1. Measure across the battery posts with the key off. A healthy battery rests at about 12.6 V. Below about 12.0 V it is flat.
2. Inspect every connection on the heavy circuit: both battery clamps, the positive cable at the starter and junction block, and the ground strap to the body and engine. White or green crust, or a clamp you can twist by hand, is enough to stop a start.
3. Clean the posts and clamps to bare metal, tighten them, and try again.
4. If you can, charge the battery fully and have it load tested. A battery that reads 12 V but collapses when the starter pulls is finished.

Wiring and help: Charging circuit (2.5i) · Power distribution

A click or chatter: battery, cables or starter

The starter solenoid is getting its signal, so the key, switch and start wiring are working. The suspects are the battery, the heavy cables and the starter itself.

1. Put a meter on the battery posts while a helper turns the key. If the voltage drops below about 9.5 V, the battery or a connection is the problem. Go back to the battery step.
2. Voltage drop on the positive side: meter between the battery positive post and the big terminal 30 on the starter while cranking. More than about 0.5 V lost means a bad cable end or connection.
3. Voltage drop on the ground side: meter between the battery negative post and the starter case while cranking. More than about 0.3 V lost means a poor ground strap or corroded engine-to-body ground. Corroded grounds are a common cause on cars this old.
4. If the battery holds up and both drops are small, the starter or its solenoid is the likely fault.

Wiring and help: Start circuit, manual cars · Start circuit, automatic cars

Slow cranking

Slow cranking is almost always electrical resistance somewhere in the heavy circuit, or a tired battery. It is rarely a wiring-diagram fault.

1. Test the battery as in the first step. A battery that is weak when cold, or after sitting, will crank slowly.
2. Do the two voltage drop tests (positive side and ground side) described under the click step.
3. If it is only slow when hot and fine when cold, heat soak in the starter is likely. Check the cable ends near the exhaust, and expect the starter to be worn.
4. Also consider the engine itself: thick oil in the cold, or something mechanically dragging.

Dash works, but the starter does nothing

With no click at all, the start signal is not reaching the starter, or the starter has no feed. This is the one case where the wiring diagram matters most.

1. Automatic cars: put the selector in P, then try N, and wiggle it. The factory diagram sends the start signal through the transmission range switch, so a dirty or misadjusted switch blocks starting.
2. Manual cars: the factory start circuit for manual cars shows no clutch switch in the path, so look elsewhere unless one was added.
3. Check fuse 10 (7.5 A). It feeds the start circuit and a long list of other circuits. If other fuse 10 items are also dead (brake warning light, back-up lights, tachometer), start there.
4. Meter the small terminal marked 50 on the starter while a helper holds the key at START. You want about 12 V.

Wiring and help: Start circuit, automatic cars · Start circuit, manual cars · Fuse data chart

No voltage at starter terminal 50: follow it back

Work backwards from the starter along the start wire until the voltage appears. The break is between the last place that has voltage and the first place that does not.

1. The start wire runs from the ignition switch terminal 50, through connector C200 pin 10, on through the 2.5 mm² wire at C101 pin 18 and a splice, to the starter terminal 50. Back-probe each connector with the key held at START.
2. Automatic cars add a start relay. Its terminal 30 comes from the ignition switch terminal 50, its coil (86) is fed through the range switch pin 9 and grounded at G200 on pin 85, and its terminal 87 carries on to the start wire. With the selector in P or N and the key at START, check 12 V on the 86 side. Voltage there but no output on 87 means a bad relay.
3. At the ignition switch, terminal 30 should be hot at all times (a 4 mm² wire through C200 pin 9). In START, terminal 50 should show the same voltage.
4. Tip: wiggle the wiring harness at each connector while a helper holds the key. A signal that flickers back is a connector.

Wiring and help: Start circuit, automatic cars · Start circuit, manual cars

Test the starter directly

This separates the starter from everything upstream of it.

1. Park on level ground with the handbrake on and the wheels chocked. Manual cars in neutral, automatic cars in P. A starter that suddenly works can move the car.
2. Use a fused jumper lead (about 10 to 15 A) from battery positive to the small terminal 50 on the starter. Touch it for a second at a time, with hands clear of belts and the fan.
3. If the engine cranks, the starter is fine and the fault is in the start wiring or switch. Go to 'No voltage at starter terminal 50'.
4. If it only clicks or does nothing, check the large terminal 30 for battery voltage and the starter case for a good ground. If both are good, the starter or its solenoid has failed.

Wiring and help: Start circuit

Starts, then stalls

Where it stalls tells you which part of the system to look at.

1. Runs only while the key is held in START, and dies when you let go: after the key springs back, the engine computer is not being kept powered or the fuel pump is not held on. Suspect the main (DME) relay and its supply, and a weak RUN contact in the ignition switch.
2. Runs for a few seconds, or dies once hot: an engine speed sensor that drops out as it heats up, or a fuel pump relay that fails hot.
3. Dies only at idle, and holds if you keep your foot on the throttle: the idle speed actuator, an air leak after the air flow meter, or a dirty throttle body.

Wiring and help: Injectors, idle actuator and sensors (2.5i)

Cranks normally but will not start

An engine needs fuel, spark, and a signal that tells the computer the engine is turning. Start with the quickest check: is the fuel pump running?

1. Check the fuel level. A fuel gauge sender can lie, so be sure there is petrol in the tank.
2. If the car has an aftermarket alarm or starter-kill switch, bypass or unplug it. They are a frequent cause on older cars.
3. Have a helper crank while you listen near the fuel tank (lift the rear seat base, or listen at the filler). You should hear a steady hum. These cars command the pump from the engine computer, so expect it while cranking and running, and perhaps a brief prime when the key goes on.

No fuel pump sound: fuses first

The pump circuit has three fuses and two relays in series, so a quick look often finds it.

1. Check fuse 11 (15 A, 'fuel delivery'), then fuses 10 and 21 (7.5 A each, both feed injection electronics). Pull each one and look, or test with a test light.
2. If a fuel pump fuse is blown, replacing it with a bigger one only hides the problem. Something is shorted or a pump is seizing.

Wiring and help: Fuse data chart · Main relay and fuel pumps (2.5i)

Bypass the fuel pump relay

This takes the relay and the computer out of the question and tells you whether the pump and its wiring work.

1. Find and pull the fuel pump relay. The relay guide shows how to read the terminal numbers and which socket holes are 30 and 87.
2. With the ignition off, connect a fused jumper between socket terminals 30 and 87. The pump should start to hum.
3. Remove the jumper straight away.

Wiring and help: How to jump a relay socket safely · Main relay and fuel pumps (2.5i)

The pump is silent even with the jumper

Now the problem is downstream of the relay: its supply, the wire to the tank, the pump ground or the pump itself.

1. With the jumper in, check the relay socket's 30 hole for battery voltage. The pump relay is fed on a 1.5 mm² wire from the battery junction block. No voltage there means a supply problem.
2. If 87 is live but the pump has nothing, the feed travels through C101 pin 13 and C114 pin 2 on its way to the pumps. Check those connectors.
3. At the pump connector, with the jumper in, measure 12 V between the feed and the pump ground. The pumps are grounded at G300 (the main and auxiliary pumps share the feed).
4. If power and ground are both present at the pump and it does not run, the pump has failed.

Wiring and help: Main relay and fuel pumps (2.5i) · Ground distribution G200 and G300

The pump works with the jumper: why does the relay not run it?

The pump, its wiring and the supply are fine. The fault is in the relay or in the signals that switch it on.

1. Swap in a known-good relay of the same type (several relays in the box are identical). If the pump now runs, replace the relay. Relays often work cold and fail when warm.
2. If a good relay does not help, test the coil. Socket 86 should show 12 V once the main relay has pulled in (it is fed from the main relay's terminal 87). Socket 85 goes to the engine computer pin 3, which grounds it when it sees the engine turning.
3. No 12 V on 86 means the problem is the main relay. 12 V on 86 but a test light between 85 and 86 stays dark while cranking means the computer is not asking for the pump, usually because it is not getting an engine speed signal.

Wiring and help: Main relay and fuel pumps (2.5i) · Swap and bench tests

The main (DME) relay

The main relay powers the engine computer, the injectors and the fuel pump relay's coil. If it fails, both the pump and the injection system go quiet.

1. Pull it and look for burnt, cracked or loose pins. Swap in a known-good relay.
2. With the ignition off, bridge socket terminals 30 and 87 with a fused jumper. That powers the computer, the injectors and the fuel pump relay coil together. If the car now runs or the pump comes on, the main relay is at fault.
3. If bridging does not help, check the socket's 30 hole for battery voltage (a 4 mm² wire from the battery junction block), and that the computer grounds the coil (85) through its pin 35 when the key is on.

Wiring and help: Main relay and fuel pumps (2.5i) · How to jump a relay socket safely

Engine speed and reference signals

The computer will not run the pump, injectors or spark unless it sees the engine turning. A failed engine speed sensor is a classic no-start with good fuel and a good battery.

1. Find the engine speed sensor (it reads the flywheel teeth) and its connector, and the cylinder identification sensor. The wiring page names their connectors. Look for oil, corrosion and bent pins.
2. Unplug the sensor and measure resistance across the two signal pins. Compare with your manual's figure. An open circuit or a dead short means a failed sensor.
3. Check the shield wire to ground. The speed sensor's shield goes to splice S700.
4. Check the sensor tip for metal swarf and the gap to the flywheel.

Wiring and help: Injectors, idle actuator and sensors (2.5i) · Ignition and air flow meter (2.5i)

Power and ground at the engine computer

Before blaming the computer, make sure it has power and a ground.

1. With the key on, check about 12 V at computer pins 18 and 37 (both come from the main relay). Pin 37 uses a 1.5 mm² wire.
2. Check the computer ground: pin 19 goes to splice S700 and on to ground. Corroded grounds are a common cause.
3. Unplug the large connector and look for green corrosion and bent or pushed-back pins. Reseat it firmly.
4. On the 2.5i, the on-board computer relay box can cut the engine computer's power (the factory documents note this as a no-start cause). Make sure its relay is not stuck.

Wiring and help: Main relay and fuel pumps (2.5i) · On-board computer relay (2.5i) · ECU ground and sensors (2.5i)

Check for spark

The pump runs, so check the ignition.

1. Pull a plug lead and fit a spare plug (or an inline spark tester). Rest the plug body on bare metal well away from the fuel system. Crank and look for a steady blue-white spark.
2. Test a few cylinders. Spark on all of them points away from the ignition. Spark on none points at the coil, its power, or the trigger signal.

No spark

Work from the coil outwards.

1. With the key on, check for 12 V at coil terminal 15. It is fed from the ignition switch through C101 pin 7 on a 2.5 mm² wire.
2. With 12 V present, the engine computer triggers the coil from coil terminal 1 (through splice S105 to computer pin 1). It will not trigger without an engine speed signal.
3. If you do get spark at the coil tower but not at the plugs, the distributor cap, rotor or plug leads are the problem. Look for cracks, moisture and carbon tracking.

Wiring and help: Ignition and air flow meter (2.5i)

Pump runs and spark is good: fuel pressure and air

Now confirm the pump is actually delivering and the injectors are firing.

1. Fit a fuel pressure gauge to the fuel rail. On these injection systems about 2.5 bar (roughly 36 psi) is typical. Confirm the figure in your manual. It should be steady and hold for several minutes after the pump stops.
2. Low or sagging pressure: clogged fuel filter, tired pump, leaking pressure regulator, or a kinked line.
3. Pressure fine: listen to each injector with a screwdriver or stethoscope while cranking. You should hear a regular tick. No tick means the computer is not pulsing them.
4. Also check the air path: a torn rubber boot between the air flow meter and the throttle body, and an air flow meter flap that is stuck.

Wiring and help: Injectors, idle actuator and sensors (2.5i) · Main relay and fuel pumps (2.5i)

Mechanical: timing belt and compression

With fuel, spark and signals confirmed, the engine itself is next.

1. If it cranks suspiciously easily or fast, remove the distributor cap and have a helper crank the engine. The rotor must turn. If it does not, the timing belt has failed or slipped.
2. Do a compression test on all six cylinders. Compare readings with your manual's spec and with each other.