| Test | TECH 1 | Notes | Nominal Values | Pin | Possible |
|---|---|---|---|---|---|
| Step | Display | Trouble | |||
| No. | Codes | ||||
| 14 | ENGINE SPEED | Engine at idle speed, | C 20 NE/NEF, 20 NE/SE/SEH, | MY '89 | 31, 19 |
| operating temperature | 20 SER; MT/AT: | 47, 48 | |||
| 720 to 880 rpm | MY '90 | ||||
| 49, 48 | |||||
| 20 SEH; MT 4x4: | |||||
| 890 to 990 rpm | |||||
| C 24 NE; MT: | |||||
| 820 to 880 rpm | |||||
| C 24 NE; AT: | |||||
| 720 to 780 rpm | |||||
| C 30 NE; MT/AT: | |||||
| 670 to 830 rpm | |||||
| C 30 SE; MT/AT: | |||||
| 570 to 730 rpm |
Note:
· In the Motronic M 1.5, trouble code 31 is always set when the ignition is ON. The code can be displayed either via TECH 1 or blinked out by short-circuiting the diagnostic plug with KM-640 in switch position "B". If the control unit receives engine speed signals from the inductive pulse pick-up during starting, trouble code 31 is automatically deleted and does not remain stored. If trouble code 31 is not deleted on starting, there is a defect present and trouble-shooting must be carried out,
· Trouble code 19 is set only during a very short interruption of the engine speed signal, with engine speeds n > 2000 rpm.
With a longer interruption and with engine speeds n < 2000 rpm, the data stream from the control unit to TECH 1 is interrupted.
Test step 14 is divided into 3 parts
A) Engine does not start, trouble code 31 remains stored
B) Short interruption of engine speed, trouble code 19 may be stored
C) Engine speed deviates from nominal values, no trouble code stored
A) Trouble code 31 remains stored during starting, engine does not start
Trouble-shooting: Nominal Value: Cause of Fault:
· Check plug connection of inductive Firm connection · Loose contact
pulse pick-up to control unit
Ignition ON
· Connect checking spark plug to Checking spark plug ignites, If no spark
ignition coil cable 4 checking lamp flashes
Connect Checking Lamp KM 602-1 to · Ignition coil defective
injection valve cable cyl. 3 · Lead interruption from
- Ignition coil to control unit Ter. 1
Start engine - Ignition coil to ignition distributor Ter. 4
· Control unit defective
If no injection signal
· Lead interruptions from
- Fuel pump relay Ter. 87 to injectors or control unit Ter. 37
- Injectors to control unit
Ter. 16 or 17
· Control unit defective
If neither spark nor injection signal
· Lead interruption from
- Pulse pick-up Ter. 1 to control unit Ter. 49 (Ter. 48 on C 24 NE MY '89)
- Pulse pick-up Ter. 2 to control unit Ter. 48 (Ter. 47 on C 24 NE MY '89)
· Check inner resistance 0.5 to 0.8 kW · Pulse pick-up defective
of inductive pulse pick-up
· Check clearance between pulse 0.3 to 1.3 mm/0.01 to 0.05 in. · Clearance too large
pick-up and segment disc C 16 SEI:
0.3 to 0.7 mm/0.01 to 0.03 in.
Further causes of trouble: · Segment disc/teeth corroded
· Metal shavings on pulse pick-up
B) Trouble code 19 or short interruption of data stream from control unit to TECH 1
Trouble-shooting: Nominal Value: Cause of Fault:
· as with A) trouble code 31 as with A) trouble code 31 · As wit trouble code 31
also
· Check segment disc for · Segment disc loose,
firm seating and damage teeth damaged
· Check ground connections from 0 W · Interference pulses in engine speed signal
inductive pulse pick-up to screening and lead
from screening to ground.
(on pulse pick-up plug on control unit side)
C)Engine speed deviates from nominal values, no trouble code stored
Trouble-shooting:
· See F0:DATA LIST, test step 18 and F5:ACTUATOR TEST, test step 01