Trolleybus MAZ-203T with autonomous running loses traction when switching to a diesel generator set (DGS), most often due to incorrect operation of the control unit ABS ECU or low charge of traction batteries. If an error message appears on the dashboard when you turn on offline mode E24 (insufficient voltage in the circuit), first check the contacts at the battery terminals and the condition of the fuse F32 (150A) in the relay box. This problem is typical for models after 2018, where an energy recovery system is installed.
Autonomous operation of trolleybuses MAZ implemented through a combined power plant: the electric motor is powered either from a contact network or from an on-board diesel generator with a power of 120–160 kW. Switching between modes occurs automatically when there is a loss of voltage in the network (below 400V) or forced by the driver through a toggle switch on the control panel. However, if after activating the autonomous mode the trolleybus stalls after 10–15 seconds, either oil pressure sensor in the diesel generator set (operation threshold - 0.8 bar), or a clogged fine fuel filter.
Design of an autonomous driving system in MAZ trolleybuses
Autonomous driving system in trolleybuses MAZ-103T/203T/206T consists of four key components:
- 🔋 Diesel generator set (DGS) - usually this is an aggregate Deutz BF4M1013 or MAN D0834 with a power of 120–160 kW, combined with an alternating current generator.
- ⚡ Traction batteries — lead-acid batteries with a capacity of 200–300 Ah, providing starting current for diesel generator sets and backup power for low-voltage systems.
- 🔄 Mode switching control unit - controller MIKAS-T or BOSCH MS6.1, which analyzes the voltage in the contact network and activates the diesel generator set when it drops below 400V.
- ⚙️ Cooling system of diesel generator set — a separate circuit with a radiator and fan, critical for preventing overheating during long-term operation on autonomous power.
Features of trolleybuses MAZ - use regenerative braking, which, when running autonomously, charges the batteries through an inverter. However, if the on-board voltage drops below 24V, the system automatically turns off recuperation to save charge for critical systems (lighting, brakes, steering). This is one of the reasons why offline mode can be jerky.
How to check the performance of a diesel generator set without a diagnostic scanner
Connect a multimeter to the generator terminals (black probe to ground, red to the “B+” terminal). When the diesel generator set is running, the voltage should be 28–30V. If the value is below 26V, check the generator belt, diode bridge or stator windings.
Typical autonomous operation faults and their causes
Most breakdowns in the autonomous trolleybus system MAZ associated with wear of the diesel generator set or problems in the electrical circuit. Here are the most common symptoms and their root causes:
| Symptom | Probable Cause | Error code (if any) |
|---|---|---|
| DGU does not start | Traction batteries are discharged, the starter or switching relay is faulty | E12, E15 |
| The diesel generator stalls after 10–20 seconds | Low oil pressure, clogged fuel filter or faulty speed sensor | E21, E28 |
| Jerks when driving autonomously | Unstable generator voltage, wear of brushes or bearings of the diesel generator set | E33 |
| Does not switch from contact network to diesel generator set | The control unit is faulty MIKAS-T or an open circuit in the voltage sensor circuit | E40, E41 |
Particular attention should be paid error code E24 - it indicates a critical voltage drop in the on-board network. In 80% of cases, the problem lies in oxidized battery terminals or a faulty generator diode bridge. If the error persists after cleaning the contacts, check the charging circuit using a tester: with the diesel generator set running, the voltage at the battery terminals should be at least 27.5V.
Diagnostics of DGU: step-by-step instructions
If the trolleybus MAZ refuses to operate independently, start diagnosing by checking the diesel generator set. Here is the algorithm of actions:
- Checking fuel and oil levels:
- 🛢️ Make sure that there are at least 20 liters of diesel fuel in the tank (the level sensor may lie).
- 🛢️ Check the oil level in the diesel generator set with a dipstick - it should be between the “MIN” and “MAX” marks.
- Fuse monitoring:
- 🔌 Find the fuse in the relay box
F32(150A) - it is responsible for the power supply circuit of the diesel generator set. - 🔌 Check the fuse
F18(10A) in the starter control circuit.
- 🔌 Find the fuse in the relay box
- Starter and generator test:
- 🔧 When you turn the key to the “Autonomous” position, you should hear the click of the starter retractor relay. If it is not there, check the relay
K12. - 🔧 After starting the diesel generator set, measure the voltage at the generator terminals: the norm is 28–30V.
- 🔧 When you turn the key to the “Autonomous” position, you should hear the click of the starter retractor relay. If it is not there, check the relay
☑️ Checklist before launching a diesel generator set
If the diesel generator set starts, but the trolleybus does not move, the problem may lie in traction motor control unit. In this case, an error is usually displayed on the dashboard E35 (no connection with the inverter). To eliminate it you need:
- Reboot the control unit by turning off the power for 30 seconds.
- Check the integrity of the cable between the inverter and the controller (it often frays around the rear axle).
- If the error persists, it is necessary to flash the control unit software (contact the service center MAZ).
If the diesel generator stalls under load (for example, when climbing), check the high-pressure fuel pump. Often the culprit is a worn plunger or a clogged coarse filter mesh.
Battery maintenance: how to extend battery life
Traction batteries in trolleybuses MAZ with autonomous movement is one of the most vulnerable points. Their average service life is 3–4 years, but if used incorrectly, it is reduced to 1–2 years. Basic rules of service:
- 🔋 Electrolyte level monitoring — check the density once a month (normal: 1.27–1.29 g/cm³ at +25°C). Add only distilled water.
- 🔌 Cleaning the terminals - oxidation increases the circuit resistance. Use a metal brush and a special lubricant (for example, Liqui Moly Batterie-Pol-Fett).
- 🔄 Regular recharging - if the trolleybus is idle for more than 3 days, connect the batteries to the charger (current - 10% of capacity).
- ⚠️ Avoid deep discharge - if the voltage drops below 21V, the batteries may lose up to 50% of their capacity.
Critical error: if after charging the batteries do not maintain a voltage above 24V for more than 10 minutes, they must be replaced. Attempting to recover such batteries with sulfation is meaningless and can lead to a short circuit in the onboard network.
For models MAZ-206T With lithium-ion batteries (installed from 2020), different rules apply:
- 🔋 Do not allow the batteries to heat above +45°C (install additional fans in the battery compartment).
- 🔌 Charge only with original charger MAZ-5432.3902 — the use of third-party devices disrupts the BMS calibration.
Diesel generator repair: when to call for service and when you can do it yourself
Some problems with a diesel generator set can be fixed on your own, but there are problems that require the intervention of specialists. Here is an indicative list:
| Malfunction | Can I fix it myself? | Tools/spare parts |
|---|---|---|
| Fuel filter clogged | Yes | Filter MANN WK820/2, filter wrench, fuel drain container |
| Generator brush wear | Yes (subject to experience) | Brushes Bosch 1 987 426 017, screwdriver, multimeter |
| Fuel injection pump malfunction | No (bench diagnostics required) | — |
| Compression drop in cylinders | No (requires a compression tester and disassembly of the diesel generator set) | — |
If DGU does not develop speed or works intermittently, first check:
- Crankshaft position sensor (contacts often oxidize).
- Injectors - when the nozzles are clogged, the engine “troubles”.
- Turbine - if it does not create pressure, the diesel generator set will “suffocate” under load.
Never ignore a mistake E21 (low oil pressure) - this can lead to jamming of the diesel generator set. If the pressure light stays on for more than 5 seconds after starting, stop the engine immediately and check the oil level.
To change oil in diesel generator sets, use only lubricants recommended by the manufacturer:
- 🛢️ For Deutz BF4M1013: Shell Rimula R4 L 15W-40 (API class CI-4).
- 🛢️ For MAN D0834: Mobil Delvac MX ESP 10W-40 (ACEA E9 class).
The volume of oil for replacement is 12 liters. Don't forget to change the oil filter (part number: MANN HU925/4 X). Replacement interval is every 500 hours or once a year.
Upgrading the autonomous driving system: what can be improved
Trolleybus owners MAZ Often they are faced with the fact that the standard autonomous driving system does not provide a sufficient range (on average 5–7 km). There are several ways to upgrade:
- 🔋 Installing additional batteries — increasing the capacity to 400 Ah allows you to extend the autonomous range to 10–12 km. However, the cooling system needs to be improved.
- ⚡ Replacing the generator with a more powerful one - for example, on Leroy-Somer LSA 46.2 (180 kW). This will increase the battery charging rate during recovery.
- 🔄 Installation of the start-stop system — automatically turns off the diesel generator set at stops, saving fuel. Suitable for models with ECU BOSCH MS6.1.
- 🛠️ Installation of an additional radiator — relevant for hot climates, where the diesel generator set overheats during prolonged operation.
When upgrading, it is important to consider that any changes in the electrical system require reflashing the control unit. For example, installing batteries with a larger capacity without adjusting the charging parameters can lead to overheating. Also note certification: not all modifications are permitted for use in public transport (coordination with the traffic police is required).
How to legalize the modernization of diesel generator sets
To make changes to the trolleybus design, you must obtain permission from the territorial department of Gostekhnadzor. You will need:
1. Technical report on the safety of modifications.
2. Test report (if the power of the diesel generator set changes).
3. Certificate of conformity for new components.
The cost of the procedure is from 50,000 rubles, the duration is 1–2 months.
Legal aspects of operating autonomous trolleybuses
Trolleybuses MAZ with autonomous movement belong to the category electric transport with a combined power plant. To use them you need:
- 📄 Vehicle registration certificate — issued after registration with the traffic police (as for buses).
- 📄 Diagnostic card - required to undergo technical inspection (every 6 months for commercial vehicles).
- 📄 Route permission — issued by the local administration if the trolleybus is used in urban transportation.
- 📄 OSAGO insurance — the minimum tariff for trolleybuses is 15,000 rubles per year.
Particular attention should be paid environmental standards. DGS in trolleybuses MAZ must comply with the standard Euro 5 (for models after 2016). If the engine does not pass the smoke test (limit - 2.5 m⁻¹), the fuel equipment will need to be replaced or a particulate filter installed.
⚠️ Attention: If the trolleybus is operated on intercity routes, it is necessary to register waybill indicating the route and operating hours of the diesel generator set. Without this document, the fine is up to 50,000 rubles (Article 12.31.1 of the Code of Administrative Offenses of the Russian Federation).
When selling an autonomous trolleybus, be sure to check:
- 🔧 Availability of a record in the PTS about modifications (if the diesel generator set was modernized).
- 📋 Certificate of the latest diagnosis of the DGU (must be no older than 3 months).
- 🔋 Condition of the batteries - if they are older than 3 years, they will require replacement (the cost of a new set is from 300,000 rubles).
FAQ: Frequently asked questions about MAZ trolleybuses with autonomous operation
How often do diesel generator sets need to be serviced?
Routine maintenance of a diesel generator set is carried out every 250 engine hours or every 6 months (whichever comes first). It includes:
- Changing the oil and oil filter.
- Check valve clearances (every 1000 operating hours).
- Cleaning the fuel system (injectors and injection pump).
For trolleybuses operating in difficult conditions (frequent ascents, high dust levels), the interval is reduced to 200 engine hours.
Is it possible to drive autonomously without a catenary all the time?
Technically yes, but this reduces the life of the diesel generator set and batteries. The manufacturer recommends using autonomous travel for no more than 30% of the total mileage. During continuous operation on diesel:
- Fuel consumption increases (up to 40 l/100 km).
- Battery life is reduced due to frequent charge-discharge cycles.
- The load on the cooling system of the diesel generator set increases.
The optimal mode is alternation: 70% of the time on the contact network, 30% on the autonomous run.
What kind of fuel should I fill into the diesel generator set?
For diesel generator sets MAZ suitable only winter diesel fuel (according to GOST 305-2013) with a pour point not higher than -35°C. Summer fuel can only be used at temperatures above +5°C. Important:
- Do not mix different types of fuel - this leads to the formation of paraffin flakes.
- Use antigel additives (for example, Liqui Moly Diesel Fliess-Fit) at temperatures below -20°C.
- Refuel only at proven gas stations - low-quality fuel destroys the injection pump.
What to do if the DGS is not gaining momentum?
If the diesel generator starts but does not rev above 1000–1200 rpm, follow these steps:
- Check air filter — clogging leads to “suffocation” of the engine.
- Diagnose turbine - if it does not create pressure, the engine will not gain power.
- Check fuel pump — when plunger pairs wear out, the pressure in the system drops.
- Make sure not air leak in the fuel line (check seals and hoses).
If the problem persists, computer diagnostics of the diesel power unit ECU is required (possibly a firmware failure or a malfunction of the gas pedal position sensor).
How much does it cost to repair a diesel generator set at a service center?
The cost of repairing a diesel generator set depends on the type of fault:
| Type of repair | Cost (RUB) |
|---|---|
| Replacing the fuel filter | 1 500–2 500 |
| Injection pump repair | 20 000–40 000 |
| Replacing generator brushes | 3 000–5 000 |
| Overhaul of diesel generator set (with replacement of piston group) | 150 000–250 000 |
Prices do not include spare parts. On average, a complete overhaul of a diesel generator set costs 300,000–500,000 rubles (depending on the engine model).