CI-132 Engine Speed (RPM) Signal
ConditionTachometer (RPM):
- Engine speed (RPM) signal missing for at least 10 seconds while the generator (GEN) transmits charging signal (D+).
Possible Source:
- Short-circuit to battery voltage in signal cable.
- Short-circuit to ground in signal cable.
- Open-circuit in signal cable.
- Open-circuit in signal cable D+ from generator (GEN).
- Contact resistance too large.
- Fault in ignition/fuel injection system.
Fault Symptom(s):
- Tachometer not working.
Start fault-tracing with step 1, below.
Checking Other Diagnostic Trouble Codes (DTCs):
Ignition On:
- Ignition on.
- Read off diagnostic trouble codes (DTCs) in fuel/ignition system.
- Is the engine speed (RPM) sensor signal diagnostic trouble code (DTC) stored?
Yes:Go to step 2, below.
No: Go to step 3, below.
2) Engine Speed (RPM) Sensor Signal Diagnostic trouble code (DTC) stored
Fault-trace according to the appropriate ALLDATA Powertrain Management Section for the relevant fuel/ignition system.
3) Checking Transmission Speed Signal:
Engine Running:
- Start engine.
- Go into scrolling values.
- Read off engine speed (RPM).
- Is the engine speed (RPM) within its permitted range?
Yes: Go to step 12, below.
No: Go to step 4, below.
4) Checking Warning Lamps:
Note: The combined instrument panel uses charging signal D+ as a reference for the engine speed (RPM) signal.
Ignition On:
- Ignition on.
- Check that warning lamps light.
- Do the warning lamps light?
Yes: Go to step 6, below.
No: Go to step 5, below.
5) Checking for an Open-Circuit:
- Check cable between combined instrument panel # A13 and generator (GEN) terminal D+ for an open-circuit. Permanent Fault
- Then continue with step 10, below.
6) Checking Engine Speed (RPM) Signal Voltage:
- Ignition off.
- Connect breakout box to ignition/engine control module. (EZ 129 K, Fenix 5.2, Motronic 4.3, Motronic 4.4 or MSA 15.7) and check ground terminals according to the relevant ALLDATA section.
- Disconnect the engine control module (ECM).
Ignition On:
- Ignition on.
- Connect a voltmeter to the breakout box as follows: EZ 129K: # 59 (# B29) and # 20 (# A20). Other engine management systems: # 21 (# B21) and # 28 (# B28)
- The voltmeter should read approx. 6 V.
If reading is OK, go to step 9, below.
If value is lower, go to step 7, below.
If value is higher, go to step 8, below.
7) Checking for Open-Circuit and Short-Circuit to Ground:
- Check cable between combined instrument panel # A11 and engine control module (ECM) # B21 for an open-circuit and a short-circuit to ground.
- On cars with EZ 129K: Check cable between combined instrument panel # A11 and ignition control module (ICM) # B29 for an open-circuit and a short-circuit to ground.
- To perform above stated checks, Permanent Fault
- Then continue with step 10, below.
8) Checking for a Short-Circuit to Supply Voltage:
- Check cable between combined instrument panel # A11 and engine control module (ECM) # B21 for a short- circuit to supply voltage.
- On cars with EZ 129K: Check cable between combined instrument panel # A11 and ignition control module (ICM)) # B29 for a short-circuit to supply voltage.
- To perform above stated checks, Permanent Fault
- Then continue with step 10, below.
9) Checking for Contact Resistance and Oxidation:
- The cause of the diagnostic trouble code (DTC) has been loose connections in the ignition/engine control module (ECM) connector. Check connector for contact resistance and oxidation and remedy. Permanent Fault
- Then continue with step 10, below.
10) Verification:
Note: After carrying out the repair check that the fault has been remedied.
- Ignition off.
Connect Connector:
- Reconnect connectors, reinstall components.
Engine Running:
- Start engine.
- Go into scrolling values.
- Read off engine speed (RPM).
- Is the engine speed (RPM) within its permitted range?
Yes: Fault is corrected:
No: Go to step 11, below.
11) Fault-Tracing Information:
- The verification result shows that the fault persists.
- Do you want to quit fault-tracing?
Yes: The fault is not corrected.
No: Start over at step 1, above.
12) Faulty Signal, Intermittent Fault:
- Check combined instrument panel connector A and engine control module (ECM) connector for loose connections and contact resistance and oxidation.
- Check cable between combined instrument panel # A11 and engine control module (ECM) # B21 for an intermittent open-circuit, an intermittent short-circuit to ground and an intermittent short-circuit to supply voltage.
- On cars with EZ 129K: Check cable between combined instrument panel # A11 and ignition control module (ICM) # B29 for an intermittent open-circuit and an intermittent short-circuit to ground.
- To perform above stated checks, Intermittent Fault
- Then continue with step 13, below.
13) Fault-Tracing Information:
- For intermittent faults fault-tracing is not followed by a verification because the fault is not present at this moment. If you want to repeat fault-tracing, start over at step 1, above.