AD30.35-L-5000A | Vehicle engine control (FMR) diagnosis, troubleshooting | 7.10.97 |
ENGINE 904 in MODELS 668, 670
Vehicle engine control (FMR) diagnosis, previous knowledge | |||
Complaint | possible cause | Note | Remedy |
Poor engine performance | PLD control recognizes: Oil pressure too low Boost pressure too low | Check oil pressure sensor (at 600 rpm >0.5 bar) When engine is at a standstill, compare boost pressure with atmospheric pressure (max. 200 mbar) | |
Too high boost air temperature Insufficient coolant temperature Too high coolant temperature | Vehicle must stand for some time (engine cooled off). Thermal cut-out is active. | Carry out plausibility check for temperature sensor | |
PLD control module faulty (host CPU failure) PLD control module faulty | Engine is in emergency mode (1300 rpm). Engine is in emergency mode (1300 rpm). | Read out fault memory for FMR control module Read out fault memory for PLD control module if necessary, check FMR parameters and actual values. Replace FMR control module as a check. | |
Solenoid valve in unit pump leaking. Crack in unit pump. Injection nozzle faulty. Connection points of pressure pipe connection leaking. | Check high side of unit pump to injection nozzle and leak fuel quantity. | ||
Fuel low pressure circuit not OK. Overflow valve leaking. Fuel filter blocked. | Check pressure in fuel low pressure circuit (5.5 to 6.5 bar) | ||
Engine brake flap faulty | Function check, visual inspection | ||
Compression pressure too low. Constant throttle faulty. | Carry out compression pressure test with STAR DIAGNOSIS (engine test). | ||
Constant throttle faulty Unit pump element sticks Unit pump drive faulty | Switch off unit pump with STAR DIAGNOSIS (engine test) individually one after the other (check engine response). | ||
Oil pressure too low | Test oil pressure | ||
Fault at turbocharger or in entire combustion air system. | Smoke limiter is active. | Check boost pressure when under load. Check air cleaner, air hoses/pipes of charge air cooler for leaks. | |
Engine surges, vibrates or runs irregularly | Accelerator pedal is not completely in rest position (closed throttle position is not reached due to foreign matter, dirt etc.). Accelerator pedal not correctly programmed. | Check instantaneous requirement of FMR (PLD actual value 02). | |
Crank angle position sensor connected wrong pole TDC sensor (camshaft position sensor) connected to wrong pole | If the engine runs better in emergency running mode, the removed rpm sensor is connected to the wrong pole. | Check polarity with STAR DIAGNOSIS routine (engine test). Disconnect crank angle position sensor or TDC sensor. | |
Accelerator pedal mechanically faulty (run out, return spring slow etc.). | Check instantaneous requirement of FMR (PLD actual value 02). | ||
Fuel low pressure circuit not OK. | Check instantaneous requirement of FMR (PLD actual value 02). | ||
Failure of high pressure part (unit pump up to injection nozzle). Leak at connection points from unit pump - pipe - pressure pipe connection - injection nozzle. | Check pressure in low pressure fuel circuit (5.5 to 6.5 bar), leak test. | ||
Excessive fuel consumption | (PLD) control module detects excessive fuel temperature. | Vehicle must stand for some time (engine cooled off). | Carry out plausibility check for temperature sensor. |
Leak at pressure side to compressor (turbocharger). | See also troubleshooting for poor performance. | Leak tightness test | |
Leak at connection points from unit pump - pipe - pressure pipe connection - injection nozzle (high pressure). | See also troubleshooting for poor performance. | Visual inspection, leak test. | |
Engine difficult to start | PLD control unit detects excessive coolant temperature | Carry out plausibility check for temperature sensor. | |
PLD control module faulty (host CPU failure) | Emergency running mode 1300 rpm | Read out fault memory for FMR control module if necessary, replace PLD control module. | |
Fuel low pressure circuit not OK | Check pressure in fuel low pressure circuit (5.5 to 6.5 bar), leak test. | ||
Solenoid valve in unit pump leaking. Unit pump faulty | Replace unit pump as a check. | ||
Injection line, pressure pipe connection or injection nozzle faulty | Check parts, replace faulty parts. | ||
Constant throttle faulty (if fitted) | White smoke after starting | Check compressed air actuation (pneumatic system). Carry out compression pressure test with STAR DIAGNOSIS (engine test). Switch off unit pumps with STAR DIAGNOSIS (engine test) individually one after the other (check engine response). | |
Engine has black exhaust | PLD control module detects: Boost pressure too high Charge air temperature too low Coolant temperature too low in the start phase Fuel temperature too high PLD control module faulty (host CPU failure) | Vehicle must stand for some time (engine cooled off). If the complaint only occurs during load/speed changes or when shifting, boost pressure and charge air temperature are the cause. Emergency running mode 1300 rpm | When engine is at a standstill, compare boost pressure with atmospheric pressure (max. 200 mbar). Carry out plausibility check for temperature sensor. Read out fault memory of FMR control module, if necessary, replace PLD control module. |
Injection nozzle faulty | Visual inspection for carbonization and blocked spray holes. Check ejection pressure stage 1 (250 bar, ejection pressure stage 2 cannot be checked). | ||
Engine brake flap faulty | Function check or visual inspection. | ||
Turbocharger faulty, charge air pipes faulty or air cleaner dirty | Visual inspection, measure boost pressure and intake pressure. | ||
Constant throttle faulty (if fitted) | Carry out compression pressure test with STAR DIAGNOSIS. | ||
Tractive power suppression | Loose contact in voltage supply Variations in voltage supply Faulty vehicle speed signal (briefly 88 km/h) | Faults are not detected by diagnosis functions in FMR and PLD control modules. | Inspect battery terminals for tight connection and corrosion. Inspect 15-pin connector at PLD control unit for corrosion and tight installation. Read out fault memory from FMR control module. Test drive with STAR DIAGNOSIS (PLD actual value 17 and 19). |
Fuel low pressure circuit not OK | Check pressure in fuel low pressure circuit (5.5 to 6.5 bar), leak test. | ||
Poor engine braking power | Fault in the FMR system | Read out fault memory from FMR control module. Check foot-operated switch (FMR actual value 29) and actuation of engine brake and if necessary, check constant throttle: When vehicle is at a standstill, briefly give "full throttle", release foot throttle actuator and quickly press engine brake foot-operated switch. If the solenoid valve switches (audible), the FMR actuation is OK. | |
Constant throttle faulty (if fitted) | Check compressed air actuation (pneumatic system). | ||
Engine brake flap faulty | Function check or visual inspection. | ||
Engine switches off unintentionally | Total failure of PLD control module | Replace PLD control module. | |
Crank angle position sensor connected wrong pole TDC sensor (camshaft position sensor) connected wrong pole | If the engine runs better in emergency running mode, the removed rpm sensor is connected to the wrong pole. | Check polarity with STAR DIAGNOSIS routine (engine test). Disconnect crank angle position sensor or TDC sensor. | |
Voltage supply interrupted | Test wiring harness with 15-pin connector. | ||
Short circuit in wiring to or at STOP button with engine running | Test pushbutton and engine wiring harness with 55-pin connector. | ||
Faulty FMR control module | Replace FMR control module as a check. | ||
Low-pressure fuel circuit not OK Drive for fuel delivery pump faulty | Check pressure in fuel low pressure circuit (5.5 to 6.5 bar), leak test. | ||
Engine becomes too hot | PLD control unit detects excessive coolant temperature | Vehicle must stand for some time (engine cooled off). | Carry out plausibility check for temperature sensor. |
Engine cuts off too soon (max. engine speed / vehicle speed is not reached) | Faulty or incorrectly parameterized FMR control module | Read out fault memory of PLD control module, if necessary, check FMR parameters and actual values. Replace FMR control module as a check. | |
PLD control unit detects engine speed too high | Check crank angle position sensor signal (distortions). | ||
Engine in emergency mode (constant rotational speed 1300 rpm) | CAN line faulty PLD control module faulty (host CPU failure, CAN processor) FMR control unit faulty | Check CAN lines for discontinuity and short circuits to one another, to ground and battery voltage+. Replace FMR control module as a check. Replace PLD control module as a check. |
Referenced documents
- ad3035l2001a Vehicle engine control (FMR) diagnosis, basic knowledge
- ad3035l4001a Vehicle engine control (FMR) diagnosis, fault memory