Electronic Diagnostics: Nissan Micra K12 1.2
Tracing and fixing faults in electronic engine management systems
Endowed with a sweet-running engine that has a good reputation for reliability, the Micra K12 can make a cost-effective used buy. But what are the diagnostic realities? Kim Henson and
Edward Haggar take a close look.
The first Nissan Micra, designation K10, was introduced in Europe in the summer of 1983, effectively replacing the Cherry as the smallest model in the line-up. By that time, Datsun/nissan had already built up a deservedly solid reputation for excellent reliability and economical operation. The less angular second-generation Micra K11 arrived in 1992, being built at Nissan’s factory in Sunderland, and a facelifted K11C version was introduced in 1997/1998. The completely restyled and curvaceous K12 made its UK debut in 2003, receiving a facelift as the K12C in 2007, which carried the model through to 2010, when it was ousted by K13.
For this feature, we are looking at a petrol-powered K12 1.2-litre (1240cc) 16-valve model registered in October 2003 (the other engine options were a 1.4 petrol unit and a Renault-derived 1.5 diesel). The well-respected engine is a transversely-mounted four- cylinder, twin-overhead camshaft 16-valve unit, incorporating chaindriven camshafts. It is fed by a multi-point fuel injection system.
Our guide to the diagnostic aspects of this engine and its ECCS management system is Edward Haggar. Preparation Although not shown in our photographs, it is useful to note that the VIN number on these Micras is visible through an aperture in the bulkhead, at the rear of the engine bay. It is helpful to quote this number when identifying the vehicle.
The engine compartment on the Micra K12 allows reasonably easy access to many of the sensors and engine ancillaries, although some are buried in the depths of the bay. The engines are highly reliable if serviced regularly and the correct oil is used. Although failure of one or more of the ignition coils is possible, it happens rarely. This engine incorporates valve clearances that are set manually. The clearances should be checked and, if necessary, reset at least every 18,000 miles or two years, whichever comes first.
Fault 1 covers dealing with a build-up of carbon around the butterfly within the throttle body assembly. In order to prevent running problems due to this, it is worth cleaning the throttle body at the same time as renewing the spark plugs. Although the motor itself is dependable, the same cannot be said of the crankshaft sensor – see Fault 2.
The engine uses a timing chain to drive the camshafts. Although this obviates the need for regular cambelt renewal, the timing chain can stretch in service over a long period. If this happens, the engine management warning lamp may be illuminated and diagnostic interrogation can reveal that a cam sensor fault code has been stored.
It is worth noting that renewal of the timing chain is not straightforward on these engines, requiring many components to be stripped in order to
reach it. With the exception of renewing the timing chain, engine maintenance and routine repairs are fairly easy.
In terms of diagnostic work, a basic fault code reader will help with entrylevel operations, such as interpreting and clearing stored fault codes, etc. However, for in-depth tasks, more sophisticated equipment such as the Snap-on SOLUS Edge diagnostic tool will be required.
Note that the ignition key assembly is easily damaged. If you need to replace
a damaged assembly, the key requires specialist equipment to programme it and not all diagnostic devices are capable of this. However, if just the buttons on the key-fob are damaged, these are easily replaced using repair kits available online.
For this Micra and other Japanese cars, high-quality components are available from Blue Print. The company started specialising in Japanese cars in 1988, but can also supply spares for European and American models.
Fault 1
CARBON BUILD-UP WITHIN THROTTLE BODY AROUND BUTTERFLY
When our first fault occurs on this Nissan, several symptoms are possible, including hesitation and poor idling of the engine, plus possible MOT test failure due to high emissions. The problem is caused by carbon build-up on the throttle body around the butterfly. The throttle body is located at the top of the engine compartment, towards the rear, as indicated in our photograph of
the engine bay. When this fault occurs it is likely that the engine management warning light won’t be illuminated, but you may find throttle position fault codes stored in the ECU.
On this Micra there is no throttle cable, with a fly-by-wire connection between the accelerator pedal and the throttle butterfly. The sticking/seizing of the butterfly in the wrong position can be the result of the ECU not receiving the correct position signal. From a diagnostic point of view, you can look at live data for throttle position, comparing this against the desired position, but the simplest method is to remove the air intake pipe and inspect it for carbon build-up.
Cleaning is simple, but be careful when you’re moving the butterfly. A toothbrush with soft bristles and some cleaning fluid does the job perfectly. Motor factors sell purpose-developed throttle cleaner, but brake cleaner fluid also works well.
On reassembly always renew the gasket. These are available for a couple of quid at your Nissan dealer.
Fault 2
AILING CRANKSHAFT SENSOR
Initially, the vehicle may cut out intermittently and then start again but, if left, the problem will escalate to complete non-starting. The fault is attributable to the crank sensor and carrying out a diagnostic assessment will show fault code ‘P0335’. If possible, look at live data for engine revs – a failed sensor will give a reading of zero. Testing at the sensor is a little difficult without the right tools, because the sensor is a three-wire digital unit.
You first need to check for battery voltage and a good earth. Next, if an oscilloscope is available, you should check the signal wire for a good signal – this is where you will see zero or a poor signal. You can also check by inserting an LED between the signal and earth – a flashing LED will show the presence of a signal, but remember you are not looking at the quality of the signal. As always, fit a good-quality replacement sensor.
Fault 3
BODY CONTROL UNIT FAILURE
When our third fault occurs, one or several of the car’s electrical circuits can behave erratically. With this model of Micra, we have experienced issues with the rear wiper not operating, but it should be noted that other circuits affected may also be those serving the central locking, electric windows, etc.
The fault is due to failure of the body control unit (Nissan call this the UCH) and you are likely to be missing the signal at the failed component. Its location is on the left-hand side of the engine bay, under the headlight. Removal of the headlamp and front bumper is required to gain access. Repair is either by replacing the unit, which will require coding, or sending the unit off for specialist repair, in which case coding will not be required.
Of course, another possible cause of the rear wiper not operating is cable breakage in the tailgate hinge, so this aspect will need checking.
Fault 4
STEERING UNIT DIFFICULTIES
The symptom for this fault can be really scary because it happens out the blue: the steering suddenly becomes exceedingly heavy and it will take a lot of strength to turn the wheel. The fault is down to the electric motor/control unit and you will see a red power steering (PS) light on the dash.
Just carrying out a diagnostic check and clearing the codes might restore operation, or you could try disconnecting and reconnecting the battery. If this doesn’t work, the units can be repaired or simply replaced and they are not coded. Most motor factors will have them in stock.