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No Start Guide

1M views 747 replies 222 participants last post by  Kolonel-Black-Fox 
#1 ·
If your car won't start, the fix can be as simple as replacing the battery, but there are many other potential causes and troubleshooting can be challenging. The following is an overview, intended to help with the diagnosis.

1. Low voltage
Bad battery
If the starter isn't cranking, or there is only a click, first check battery voltage with a digital multimeter (see photo in post 39), or using the OBC hidden functions (see info in post 37).
It needs to be at least 12V for the starter to be able to crank, while full battery voltage is close to 12.6V.
Faulty alternator
The battery may have died because the alternator isn't charging it.
To test the alternator, first start the car by charging the battery, by jump start, or push start. Measure battery voltage with the engine running, it should be close to 14V, or slightly over.
Bad connections
If the battery and alternator are OK, but voltage is low at the starter, there could be a loose, or corroded connection in the electrical system, causing a voltage drop. Check the ground strap under the engine on the passenger side and the battery terminals. The battery safety terminal (BST), located on the positive battery terminal, is designed to cut off power to the engine in case of an accident. If voltage is sufficient at the battery, but low at the underhood jumper terminals, there is a bad connection at the BST. (see photo in post 60)
Parasitic draw
If the engine runs fine when the battery is charged, or after a jump start, but the battery is dead by morning, there could be a short in the system draining the battery overnight. This is referred to as parasitic draw and on the E46 it is usually caused by a faulty final stage resistor (FSR) of the blower motor. Aftermarket equipment is another common source of parasitic draw.

2. Fuel related
Fuel pump
If the starter is cranking, but the engine isn't starting, the most likely issue is the fuel pump. There are a number of ways to verify.
  • listen for the pump to prime when key is turned to position #2
  • check for fuel at the fuel rail at the Schrader valve
  • measure the actual fuel pressure (or lack thereof) at the rail, it must be 50 PSI
  • spray starting fluid into the intake, if the engine stars briefly, fuel isn't reaching the engine.
You can also remove the fuel pump cover and whack the pump, this may get it going temporarily. This "method" can come in handy if you're far away from home.
Engine is flooded
The M54 engines flood easily if they are started and run for a short time, like moving from one parking spot to another. If the engine won't start shortly thereafter, the spark plugs might be saturated with fuel, preventing spark. No start at a later time may be due to loss of compression. See Section 6. for more info on that.
No gas in tank
If the engine stalls, or will not start when the gas is under ¼ tank, the fuel pump is weak and should be replaced. The gas tank has two lobes and a weak pump isn't able to transfer fuel from the other lobe. Fuel gauge maybe inaccurate, reading too high.
Bad gas
No start after the car was sitting for a long time. If your car runs rough and/or won't start right after filling up with gas, the fuel might be contaminated.
Fuel filter
A clogged, or restricted fuel filter usually causes engine performance problems, but it can also contribute to no/hard start.
Fuel pressure regulator
On the 325i/330i this is part of the fuel filter, so by replacing the filter, the FPR will also be renewed. On the 323i/328i it's separate from the filter. These rarely fail on the E46, but it's a possibility. No start due to no, or low fuel pressure can be caused by a defective fuel pressure regulator.

3. Starter
If battery voltage is sufficient at the starter's electrical connections and the starter is not cranking, it is most likely defective. Replacing the starter isn't easy, so make sure the diagnosis is correct before you undertake this task.
Suggestions for troubleshooting: remove the airbox and the intake boots to gain access to the starter. Measure voltage on two of the terminals on the starter solenoid. Terminal "B" should have constant battery voltage. Terminal "C" is energized by the ignition switch via EWS module when starting the engine. Remove the wire from this terminal, measure voltage on the wire with the key in start position.
Motor vehicle Coil Automotive fuel system Gas Auto part


If sufficient battery voltage is present at both terminals and the starter isn't cranking, it is defective. You can also test the starter by jumpering, or "hot wiring" it. This is done by applying direct voltage to some of the terminals. When voltage is applied to terminal "D", the starter motor should spin without cranking the engine. When voltage is applied to terminal "C", the starter should crank the engine. Make sure you have good engine to chassis ground. Sometimes there is a bad connection at the ground strap that is under the engine on the passenger side. The starter can also get stuck. If voltage is sufficient, but the starter only clicks, this may be the case. Tap the starter while a helper attempts to crank the engine. If it is stuck, this may get it going.

4. Switches and sensors
Ignition switch
If there is no power at terminal "C" on the starter with the key in the start position, there is either an EWS problem, or a bad ignition switch. A faulty ignition switch can cause either a no crank/no start, or crank/no start condition. Intermittent no start, or strange electrical symptoms are also typical signs of a failing ignition switch. Wiggle the key as you start the car, that sometimes works if the switch is bad.
Cranks but no start
Check battery voltage at fuse 29 while starting. This is the ignition switch input to the DME. (see photo in post 60). Check battery voltage at pin 15 on the coil harness with the ignition on. (see photo in post 61). Warning lights going off on the dash randomly, or suddenly while cranking is an indication of a faulty ignition switch.
No crank
Check battery voltage on the black/blue wire at the ignition switch connector with the key in the start position. This wire supplies voltage to terminal "C" on the starter via the EWS module while starting. No voltage in any of the tests indicates a defective switch.
Clutch switch
A defective clutch switch, (or not pressing the clutch pedal far enough) will prevent starting. If battery voltage is OK and starter doesn't crank, this is one of the possible issues. To test the switch, bypass it by inserting a jumper wire in its connector. (wires violet/yellow and black/blue) Switch designs vary throughout the years.
Auto (neutral) safety switch
This is the equivalent of the clutch switch on an automatic, it allows the engine to start only in "P" and "N".
The gear selector switch, located on the side of the transmission performs this function.
Move the shifter back and forth a few times before starting, this may enable start, if the switch is faulty.
Crank position sensor
The DME needs the signal from this sensor to fire the plugs. A faulty crank sensor usually throws a code, making diagnosis simple. If there is no code stored for this sensor, but no spark is suspected, check for spark. See post 62 for info on how to check for spark. If there is spark, the crank sensor must be doing it's job. If there is no spark and no crank sensor code, look at the tachometer while cranking. If the sensor works, the needle should read about 200 rpm.
Camshaft position sensor
A defective cam sensor most often results in driveability problems, like stalling, loss of power and rough running, but it can also prevent the engine from starting. This usually causes CEL, too.

5. Fuses, relays and modules
Immobilizer (EWS)
A faulty EWS module, a key that is not coded to the module, or damaged will prevent the engine from starting. There won't be any power at terminal "C" on the starter solenoid, resulting in a no crank condition. If you hear a beep with the key in the ignition and the driver's door open, the EWS is recognizing the key. Trying to start the car with a second key is another simple way of ruling out a no start due to a non working key. A scan with a BMW specific scanner is necessary to detect EWS faults. If your car is equipped with an additional aftermarket alarm system, make sure it is disarmed.
Fuses
E-box fuse pack

Under the hood on the driver's side where the DME and other electronic components are located, there is a fuse pack, containing 5 fuses. These are related to engine management. Fuse #3 sends power to both fuel pump relay and the crank sensor. (see photo in post 142)
Main fuse panel
Check fuses 9, 22, 27, 29, 30 (ignition switch), 54 (fuel pump), and 14, 49, 67 (EWS). Inspect all fuses in the glove compartment if you're dealing with a hard to diagnose no start problem. Check the high amp fuses above main fuse panel (fuseable links). There is an 80 amp for the DME and DME main relay, and a 50 amp fuse for the ignition switch. Check the harness fuse: behind the carpeting on the passenger side shock tower there is a large fuse. The cable here supplies the relay panel, so if this fuse is blown, almost everything will be out.
DME Relay
Unlike the older models, this isn't problematic on the E46. Test this relay if there is no battery voltage at the E-box fuses. See post 408 for info on trouble shooting!
Electronic Control Unit (DME)
DME failure is also not common, but possible. A scan with a BMW specific scanner usually reveals if the unit is faulty. There may be no codes stored. If there is no spark, or injector signal and all DME inputs and wiring are OK, the DME needs replacing.
Fuel pump relay
No power at the fuel pump may be caused by a bad fuel pump relay. When checking for power at the pump, the engine needs to be cranked. A simple test for the fuel pump relay is to swap it with the horn relay, they are identical. Additional electrical tests can be done by jumpering terminals at the relay board. If the pump runs with the terminals jumpered, but not with the relay in place, the relay is defective.

6. Mechanical issues
No compression
An engine needs spark, fuel and compression to run. If there is both spark and fuel and your car won't start, test engine compression. At times a condition called cylinder wash down occurs. If the engine started and run for a short time, or when an engine is cranked without starting, a lot of fuel is dumped into the cylinders. This can wash the oil off the cylinder walls and lead to loss of compression. Pour some oil in each cylinder, this will restore compression.
Camshaft timing
The timing chain assembly is reliable on the 6 cylinder engines, but can be problematic on the 4 cylinders models.
Engine seized
An internal mechanical failure can cause the engine to lock up. Try to turn the crankshaft manually to see if the engine is frozen.
Hydrolock
The crankshaft can not rotate due to liquid in the combustion chamber. This can be fuel, coolant, or oil, caused by a leaking fuel injector, head gasket, or a malfunctioning CCV system. Remove spark plugs and crank the engine if this is suspected.
Vacuum leak
Vacuum leaks usually cause rough running, or misfires, but a large vacuum leak can prevent starting. If your car won't start after working around the intake, this is the most likely problem. In this case the engine may start up momentarily, but stalls immediately.
 
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#37 · (Edited)
When you turn the key and the lights come on on the dash, that is position 2, or ignition on. The fuel pump primes for maybe 2 seconds. The fuel pump is under the rear seat on the right side. If you listen carefully as you turn the key, you should hear the fuel pump.

If the starter doesn't crank, first you need to measure battery voltage.
Use a multimeter, or learn to display voltage on the OBC.

Instructions to access the hidden OBC functions:

1. Hold Trip Reset while turning ignition key to on position
2. OBC should show "Test"
3. Use Trip Reset to select function 19.0 that unlocks all the features
3. Wait for display to show "Off"
4. Depress Trip Reset for 1/4 second and release it
5. With no delay press Trip Reset several times to #9

You can now see system voltage.
 
#43 · (Edited)
your battery sounds very weak. Even if it's cranking, it may not be enough to start the car. Had a similar problem recently: http://forum.e46fanatics.com/showthread.php?t=1030425&highlight=. Car was cranking so I ignored the battery, but these cars need a strong battery to turn the engine over quickly enough to start.

test the theory by having someone give you a jump. If that doesn't work, have the battery charged, try again, and report back.
 
#41 ·
If it cranks, you may need a fuel pump. Remove the rear seat, that way it's easier to hear the pump prime. Pull on the corner of the seat firmly on each side.
The fuel pump is under the round cover. When you turn the key to position 2, you should hear a short buzzing sound.
 
#46 ·
Hey if I pop out my wires for the exhaust cam position sensor, should oil have gotten into that plug area?? Or should it be bone dry, and oil only appear when I pull the sensor out?

I can't run codes, just replaced my fuel pump and still can't start, and noticed that when checking that sensor. New alt,battery(49), and fuel pump. Cranks strong but won't turn over.




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#48 ·
What made you so certain from the start lol. I just started a thread, with pictures. Im certain it didn't drip "on" to it because it was directly in the plug. But also I am led to believe it's my issue because I had the slow acceleration in low rpms, and had all the stalling under 40 randomly and the not 100% consistent slow starts. But it didn't wind up being the fuel pump, I am check the filter. But why would the original sensor have oil directly in it if it's not suppose to, seems to me that could cause the sensor to act funny depending on how much oil got to it at the time of use could be the reason for the fluctuation in problems. But, I don't have the tools to test it right now, but did have a CEL.




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#54 ·
No clue actually. And look

Auto part Engine Vehicle Automotive engine part Automotive fuel system

Auto part Fuel line Engine Automotive fuel system Suspension
Auto part Vehicle Engine



I electrical taped over all the colours to the tubing to protect those better. They aren't brittle. But I also cut and found where the wires on the intake cam sensor were healthy, re wired and fixed up enough to get me to the shop for a new one.

Is running the wires to my exhaust cam sensor and other two plugs, safe to run from the engine > up through the gap between the oil filter and canister(unbolt and rebolt canister, wires are not tight fit) > along the front the engine to the plugs/sensors?


I'll post a picture of what I mean later




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#55 ·
My M3 wouldn't start today. Got in the car, clutch in, turned the key. Everything was fine till I turned to ignition. Once I went to start it, the instrument cluster and all the electrical died, no click from the starter, it all died.

Got out, popped the trunk, checked the battery for a loose terminal or something obvious. Wiggled the negative terminal, but it was tight. Saw the cabin light come on, got in, tried again. Same thing. All looks good until I try to turn it over, then electrical dies, just as before.

Jumped in my Acura and found this guide at work, I'll give the troubleshooting you posted when I get home.

Any preliminary guesses?
 
#56 ·
Is the ground wire that's attached to the battery, well attached on the other side? Most of the time we only think to check the battery, not the other side of the wire.

You might have a problem like mine directly above yours in this post, where wires are shorting out.

You can also check the computer in your dash if it's working, going to 19 off, 9, and check alternator voltage with it, and the rest of your cars voltages




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#62 · (Edited)
How to check for spark

It's possible to check for spark either at the coil, or spark plugs.

How to check for spark at the coil

Disconnect one of the coil harnesses and find pin 1. This is the signal wire from the DME. Reconnect it and pull the rubber boot back. Connect a test light to pin 1. from the back of the harness. Have someone to crank the engine. The test light should flash, indicating spark at the plug.




How to check for spark at the spark plugs

Remove a coil and spark plug. Reconnect the coil harness and place the plug back in the coil boot. Here I'm using vice grips with a slight tension to hold the plug stable in the boot. I am grounding the plug with jumper cables.
Have someone crank the engine, or position the coil/plug in such a way that you can see it from the cabin.
In this case I was able to see the plug and spark by turning the key from the passenger seat.

 
#63 ·
Just to share:

My 328i has the habit of no start, no crank after engine warmed up or sitting under the sun for more than an hour. Cold start is not a problem, engine fires right up whenever I turn the key.

This behaviour has been consistent for the past few months so I took it to BMW for diagnostics. They found that under the no start condition, there is no signal to the starter from the EWS so they recommend to replace the EWS.

Hence my car is sitting in BMW waiting for a new EWS shipped from Germany now. I know somebody has said that I can by-pass the EWS to always give signal to the starter whenever the key is turned but the price they charged for the job is not that expensive so I gave them a go.
 
#65 ·
In my 2001 e46 330M the coolant temp sensor caused the engine to "flood" and not start.

Copied this from a temp sensor thread...

Hi all new to the forum and Beemers. Now have an e46 330msport and love the car. Recently had some issues with car and found this thread. Also having troubles with hard starting and temp gauge issue. Using a generic code reader found dtc's for the temp sensor and cam sensor. I first replaced the cam sensor, there was an improvement, and it seemed to be starting fine for a couple weeks. But again the car would not start and would take an hour or more before re-starting. I found that the temp senor was reading full cold when the car would not start. This makes the computer think it's -40 f and rich-ens the mixture enough to foul the plugs. I also have new and correct ngk plugs in. I have been a tech for 20+ years with Saab, Subaru, GM as well as customs, racing cars boats etc. with fuel injection and am now learning about my bmw. Sounds to me like the original question was confused by the "mechanic" who does not know bmw's. The ECT engine coolant temp sensor sends a signal to the computer and controls the gauge, it is in the cylinder head below #6 intake port. This has nothing to do with oil temp. There is also a coolant temp sensor in the lower radiator hose, for fan control only. Now for the good part, I was able to change the sensor without removing the intake. It is difficult but using a deep 22mm socket a universal and a wobble extension I was able to replace it by just removing the cowl in well under two hours. The car now runs great again and starts every time, really a great car

Spark/timing, air, fuel, compression, find which is missing and your well on your way...




 
#66 · (Edited)
Thanks for the info!
I remember this being a common problem with the older cars.
One of the first parts I replaced on my E28 when it didn't start was the CTS.

Engine is flooded due to a faulty coolant temperature sensor.
The temperature gauge reading cold with the engine warm can be a giveaway.
 
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