Typical BMW 1-Series components

1 The positive jump-start connection point (protected by the red plastic cap) is located adjacent to the engine bay’s rear bulkhead, close to the righthand side. Connect the positive lead via this point, not directly to the battery. 4 An additional important earth connection point is located at the left-hand inner wing. It’s vital that the connection is clean and not corroded. Note that the plastic protective shield can crack, allowing the ingress of moisture which leads to corrosion. 2 The negative jump-start connection point is found next to the right-hand inner wing. Again, when connecting up a negative cable or lead from a jump pack, always use this earthed connection point, rather than the negative battery terminal. 5 The mass air flow (MAF) sensor is mounted within the intake trunking. Its function is to monitor the rate of air flowing through the system, sending this information to the ECU, which in turn calculates and adjusts fuelling levels accordingly. 3 There’s a vital earth connection point on the right-hand side of the chassis. Problems arise if there is dirt/ corrosion around this, including diagnostic equipment not reading. We advise cleaning the connection point and using a silicone spray to coat and protect it. 6 The electronic throttle body is also situated within the intake trunking. By contrast with earlier set-ups in which there is a direct mechanical linkage between the accelerator pedal and the throttle body, the two are connected electronically in this system.

1000 actuations the system determines that the lock is worn and needs to be renewed. If the car is then taken to BMW, they sell the driver a new steering column and recode it, but in our experience the counter just needs to be reset to restore full operation, although there are further aspects to consider regarding the battery voltage and the car’s keys.

If the car starts sometimes but fails on other occasions, it could be that the battery has a weak cell, so get the battery checked and renew it if in any doubt.

Another important point: it’s essential that when the ignition key is placed in its dashboard slot, an audible clunk is heard, indicating that the lock has been released. These keys are easily damaged and should be treated with respect in order to avoid trouble.

While on the subject of electrical ailments, if you find that the clock and radio have reset for no obvious reason, it’s likely that the AGM (Advanced Glass Mat) battery may be suffering from corroded terminals, which can result in strange issues. This can be due to water ingress into the boot (see Fault 2). Don’t be tempted to fit a standard battery as this will quickly fail.

Fault 2

DEFECTIVE PARKING SENSOR ECU

When our second fault arises, there will be no running issues but you will see an annoying illuminated amber light with a ‘P’ on the dash, and the parking sensors might not work or begin behaving erratically. The component at fault is the parking sensor ECU located on the right-hand side of the boot, behind the battery. It’s likely that you will find it fully sitting in water.

The first step to restore operation is to remove the unit and dry it out – possibly an evening in an airing cupboard may

fix it. Remember that the water leak will need to be identified before refitting the unit, and there are numerous points where water can leak in, from rear lights to boot seals. The unit isn’t coded, so a sound secondhand unit could be an option if your waterlogged one doesn’t respond after drying out.

Fault 3

FAILED TRACTION CONTROL SYSTEM ECU

This fault can show itself by way of the ACS/DCS traction control warning lights being illuminated. Again, this will cause no running issues.

Carrying out a diagnostic check will show the code ‘5E20 – hydraulic pressure sensor internal’. This isn’t actually a sensor fault, but an error within the ECU serving the traction control/abs systems and the ECU will require replacing or reconditioning (there are many reliable ECU repairers out there who can refurbish the existing unit). The benefit of reconditioning is that no coding will be required, whereas a replacement unit will need to be coded.

Fault 4 TIMING CHAIN FAILURE

Our last fault with this 1-Series relates to the timing chain. As with BMW’S diesel power units, these petrol engines are prone to timing chain problems/ failure. Worryingly, they can fail with no prior warning and leave you stranded. If the chain ends up breaking, it’s highly likely that valve damage will occur, causing a costly repair or a vehicle write-off given the expense of parts and labour. It’s almost worth replacing the timing chain as a service item to rule out any problems in the future.

Replacing the chain on the petrol engine is easy compared to the diesel, with a competent mechanic only needing a locking set to do it.

This fault can sometimes cause lack of power and rough running because the ECU detects a difference in the cam and crank signal. Carrying out a full diagnostic check will show fault codes relating to cam sensor timing.

If your tester allows you to carry out a cam/crank synchronisation check it could pass or fail. If available, using a cam and crank scope to verify the fault can be useful.