Diesel engines Nissan with control system KMU (Keihin Motor Unit) is a separate category of power units that were installed on the brand’s commercial and passenger models in the 1990–2000s. These engines were famous for their reliability, but they also had specific “diseases” associated with the electronic control unit of the fuel pump. If you are the owner Nissan Terrano, Pathfinder, Navara or Patrol with diesel TD27, TD42 or ZD30, this article will help you understand the intricacies of the work KMU, typical malfunctions and methods for eliminating them.
System KMU - this is a joint development Nissan and companies Keihin, designed to optimize fuel supply in diesel engines. Unlike classic mechanical fuel injection pumps, here an electronic unit is responsible for control, which allows for more accurate fuel dosing and reduced consumption. However, over time KMU becomes a source of headaches: unit failures, sensor errors, startup problems. In this article we will look at how to diagnose faults, where to look for spare parts and whether it is possible to do without expensive repairs.
What is KMU in diesel Nissans and how does it work?
Abbreviation KMU stands for Keihin Motor Unit — an electronic module integrated into the high-pressure fuel pump (HPF). Its main task is to control the supply of diesel fuel to the cylinders based on signals from sensors:
- 🔹 Crankshaft position sensor — synchronizes injection with the operation of the pistons.
- 🔹 Coolant temperature sensor — adjusts the mixture composition during a cold start.
- 🔹 Air pressure sensor — takes into account the load on the engine.
- 🔹 Accelerator pedal position sensor - regulates speed.
Unlike mechanical injection pumps, where the fuel supply depends on springs and centrifugal weights, KMU uses solenoids And electronic valves. This allows you to:
- 🔸 Reduce fuel consumption by 5–10%.
- 🔸 Improve acceleration dynamics.
- 🔸 Reduce emissions of harmful substances (relevant for standards
Euro-2/Euro-3).
However, electronic filling also has disadvantages: KMU sensitive to fuel quality, voltage drops and mechanical vibrations. For example, water getting into a diesel engine or corrosion of contacts can damage the unit, and its repair costs 30–50% of the cost of a new pump.
If your Nissan with KMU suddenly stalled and won't start, first check the fuse EF15 (15A) in the block under the hood. Its burnout is a common cause of system shutdown.
Typical KMU malfunctions and their symptoms
Problems with KMU manifest themselves in different ways, but there are a number of “classic” signs that should alert you:
| Symptom | Probable Cause | Diagnostic method |
|---|---|---|
| The engine does not start, the starter turns | Unit failure KMU or power supply interruption | Checking the voltage at the pump connector (should be 12V) |
| Floating idle speed | Pedal position sensor is dirty or solenoid is faulty | Cleaning the contacts, testing the solenoid with a multimeter |
| Exhaust smoke (black or bluish smoke) | Fuel overflow due to incorrect sensor signals | Diagnostics with a scanner (errors P0251, P0252) |
| Loss of power, “dips” during acceleration | Worn plunger pairs or clogged fine filter | Measuring pressure in the fuel rail (standard: 200–250 bar) |
One of the most common problems is contact corrosion on the connector KMU. Due to moisture and salts (especially in winter), the pins oxidize, which leads to signal loss. In this case, cleaning the contacts helps. WD-40 or contact lubricant, but if the corrosion is deep, the connector will need to be replaced.
⚠️ Attention: If after washing the engine Nissan stopped starting, never dry it KMU hairdryer or compressor! Overheating the unit can damage the microcircuits. Allow the system to dry naturally for 12 to 24 hours.
KMU diagnostics: tools and algorithms
To check KMU you will need:
- 🔧 Multimeter (for measuring voltage and resistance).
- 🔧 Diagnostic scanner (for example, Launch CReader or ELM327 with the program Nissan DataScan).
- 🔧 Compression gauge (to check the pressure in the cylinders).
- 🔧 A set of socket wrenches (for dismantling the injection pump).
Diagnostic algorithm:
- Checking the power supply. On the connector KMU (usually 3-pin) should be
12Von one of the contacts when the ignition is on. No voltage indicates an open circuit or a faulty fuse. - Sensor test. We use a scanner to read errors (for example,
P0190— malfunction of the fuel pressure sensor). - Checking solenoids. The winding resistance must be within
0.5–5 Ohm(see the manual for your model for exact values). - Pressure control. We connect the pressure gauge to the fuel rail: when starting, the pressure should rise to
200+ bar.
If the scanner shows an error P1230 (“Fuel injection pump control circuit malfunction”), this may mean:
- 🔸 Break or short circuit in the wiring harness.
- 🔸 Malfunction of the unit itself KMU.
- 🔸 Problems with the “ground” (check the fastening of the negative wire to the body).
- Multimeter
- Diagnostic scanner
- Laptop with program
- I contact the service
Repair or replacement of KMU: what to choose?
Cost of a new block KMU for Nissan TD27 or TD42 amounts to 80–150 thousand rubles., and repairs cost 20–40 thousand rubles. (depending on complexity). Which is more profitable?
Repairable faults:
- 🔧 Replacement of solenoids (if the winding is intact and the problem is in the mechanical part).
- 🔧 Restoring contacts on the board (soldering, replacing resistors).
- 🔧 Cleaning or replacing the pump shaft position sensor.
When replacement is needed:
- 🔧 Burnout of microcircuits (visible by blackened tracks on the board).
- 🔧 Cracks in the block body (lead to fuel getting inside).
- 🔧 Complete failure of the electronic part (the unit does not respond to scanner signals).
In Russia there are several specialized workshops that carry out repairs KMU (for example, in Moscow - "Diesel Master", in St. Petersburg - "Nissan-Service"). The average repair time is 3–5 days. If you decide to replace, pay attention to contract pumps from Japan (they can be found at salvage yards for the price 30–60 thousand rubles.), but make sure the block matches the part number (for example, 16600-4M000 for TD27T).
☑️ Before buying a used KMU, check
Preventing problems with KMU: tips for owners
To extend life KMU, follow these guidelines:
- Use quality fuel. Diesel with a high sulfur or water content accelerates wear of plunger pairs and corrosion of contacts. Refuel at trusted gas stations (for example, Gazpromneft or "Lukoil").
- Change the fuel filter every
10–15 thousand km. A clogged filter increases the load on the pump, which leads to overheating KMU. - Check the ground. Oxidation of the negative cable on the body or battery can cause voltage surges that are harmful to electronics.
- Avoid deep puddles. Water getting into the connector KMU - one of the main reasons for its failure.
It is also useful to carry out once a year preventative cleaning block contacts. To do this:
- Remove the connector from KMU (having previously disconnected the negative battery).
- Treat contacts with cleaner CRC or WD-40.
- Apply a thin layer dielectric grease (For example, Liqui Moly).
⚠️ Attention: Never use to clean contacts KMU acetone or gasoline! These solvents destroy the plastic of the connector and leave a film that impairs conductivity.
How to check KMU without a scanner?
If you don't have diagnostic equipment, you can try the following method:
1. Disconnect the connector from the unit KMU.
2. Turn on the ignition and use a multimeter to measure the voltage between the positive contact and ground (should be 12V).
3. Reconnect the connector and try to start the engine. If the pump does not make a characteristic buzzing sound, the problem is in the unit or power supply.
Alternative solutions: is it possible to do without KMU?
Owners of old Nissan with KMU People often ask the question: is it possible to convert the system to a mechanical fuel injection pump or install another electronic unit? This is theoretically possible, but in practice it is fraught with difficulties:
- 🔹 Transition to a mechanical injection pump will require replacing the pump, receiver, as well as flashing the ECU (if there is one). The cost of such alteration is from
100 thousand rubles.. - 🔹 Installation of fuel injection pump from another model (for example, from Toyota or Isuzu) is possible, but will require modifications to the fasteners and fuel lines.
- 🔹 KMU signal emulation using an external control unit (for example, "Diesel Control") is an option for experienced electricians, but does not guarantee stable operation.
The most rational way out is repair of native KMU or purchasing a contract block. Rework is only justified if you are willing to invest time and money in rework, and also have access to turning and welding.
Example of a successful remodel: owners Nissan Terrano II with motor TD27ETi install fuel injection pump from Isuzu 4JG2, but this requires:
- 🔧 Making an adapter plate for the pump.
- 🔧 Replacing fuel hoses with more durable ones (withstanding pressure
300 bar). - 🔧 Setting the injection advance angle (a stand will be required).
Reworking the injection system with KMU for a mechanical injection pump is only suitable for experienced mechanics. In 80% of cases it is cheaper and more reliable to repair the original unit.
Where to buy spare parts for KMU and how much it costs
Spare parts for KMU can be found in the following places:
| Detail | Where to buy | Average price, rub. |
|---|---|---|
| Solenoid KMU | AliExpress, eBay (original Keihin) | 3 000–6 000 |
| Power connector | Car dismantling yards, electronics stores | 1 500–4 000 |
| Repair kit for plunger pairs | Specialized workshops (for example, Diesel-Plus) | 8 000–15 000 |
| KMU unit (used) | Japanese showdown (JDM Parts) | 30 000–60 000 |
| Control board (repair) | Diesel electronics repair workshops | 10 000–25 000 |
When buying used KMU be sure to check:
- 🔹 Part number (must match your pump).
- 🔹 Condition of the shaft (there should be no backlash).
- 🔹 Availability of a label with the production date (old blocks may have worn solenoids).
If you are looking for original spare parts, pay attention to the following articles:
- 🔹 Solenoid KMU for TD27:
16640-4M000. - 🔹 Shaft position sensor:
23731-4M000. - 🔹 Power connector:
24880-4M000.
To save money, you can consider analogues from Bosch or Denso, but their compatibility needs to be clarified with the seller.
FAQ: Frequently asked questions about KMU in diesel Nissans
Is it possible to drive with a faulty KMU?
No, it's dangerous. A faulty unit can cause uncontrolled fuel injection, which will lead to water hammer (piston breakage) or a fire due to diesel leakage onto the hot manifold. At the first sign of a malfunction (jerking, smoke, startup failure), immediately diagnose the system.
What resource does KMU have?
When used correctly, the unit KMU serves 200–300 thousand km. However, the resource depends on the quality of the fuel, timely maintenance and operating conditions. In northern regions, electronics fail faster due to low temperatures.
Can I repair KMU myself?
Partially yes. For example, even a beginner can clean the contacts or replace the solenoid. But to solder boards or adjust plunger pairs, you need special tools (soldering station, stand for high-pressure fuel pumps) and experience. Without them, the risk of finally breaking the block is very high.
What to do if the KMU is “flooded” with fuel?
If diesel fuel gets into the unit (for example, due to a crack in the housing), it needs to be disassembled and washed isopropyl alcohol and dry for 24 hours. After this, check the resistance of the solenoid windings - if it has changed, the part must be replaced.
Where can I find the KMU wiring diagram for my model?
Schemes can be downloaded from forums (for example, "Nissan Club" or "Dieselist") or in service manuals (Nissan Service Manual). For TD27 And TD42 The circuits are usually the same, but may differ in connectors.