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Home / DTC / B1368 — Ignition system tachometer signal output circuit open

B1368 — Ignition system tachometer signal output circuit open

Detailed page for trouble code B1368.

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Code

B1368

ALFA ROMEO B — Body

Ignition system tachometer signal output circuit open

Brand: ALFA ROMEO
Type: B — Body
AI status
Completed
ready
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Page language: EN

Causes

  • Open or broken wiring between ignition/ECU and instrument cluster
  • Disconnected, corroded or damaged connector/pins
  • Blown fuse or faulty relay feeding ignition electronics or cluster
  • Faulty ignition control module, coil pack tach output or engine ECU
  • Failed instrument cluster input circuitry
  • Poor ground or battery connection affecting signal reference

Symptoms

  • Tachometer needle does not move or reads zero
  • Possible intermittent or no RPM input to other systems that use tach signal
  • Engine runs normally (often) while instrument cluster shows no RPM
  • MIL may not be present specifically for engine misfires (this is a signal/circuit fault)
  • Possible communication or limp-home behavior if other modules rely on the tach

What to check

  • Read and record all stored DTCs; clear codes and attempt to re-create B1368
  • Visually inspect wiring, connectors and ground points between ignition coils/ignition module, ECU and instrument cluster
  • Check relevant fuses and relays for continuity and correct supply voltage
  • Backprobe tach signal pin at the instrument cluster and at the ignition/ECU connector
  • Measure continuity between the cluster pin and the ignition/ECU/coil tach output pin with ignition off
  • Check for correct reference ground and battery voltage at related modules

Signal parameters

  • Type: pulsed square wave (ignition/coils or ECU-generated) proportional to engine speed
  • Amplitude: commonly 0–5 V or 0–12 V depending on vehicle electronics (confirm in factory data)
  • Frequency: proportional to engine RPM and number of ignition events per engine revolution (consult service manual for pulses-per-rev)
  • Idle example: low-frequency pulses (typically a few Hz to a few tens of Hz depending on engine), rising with RPM
  • Reference: signal should be present at the source (coil/ignition module/ECU) and the same (or slightly attenuated) at the cluster input

Diagnostic algorithm

  1. Scan and record all codes; note any related network/cluster codes. Clear codes and see if B1368 returns.
  2. Visually inspect wiring harnesses and connectors for damage, corrosion, loose pins between ignition module/coil, engine ECU and instrument cluster. Repair any damage.
  3. Verify fuses/relays supplying the cluster and ignition electronics. Replace any blown fuses and retest.
  4. With ignition ON (engine off) backprobe the tach output pin at the ignition module/coil or ECU and at the cluster input. Check for expected voltage reference and pulses while cranking/ running.
  5. Use an oscilloscope to confirm pulse waveform and continuity. If pulses are present at the source but absent at the cluster, locate break in wiring and repair.
  6. If no pulses at the source, isolate whether the ignition coil/module or ECU is the origin by checking upstream connectors and grounds; test or substitute the ignition module/coil if appropriate.
  7. If wiring and source test OK but cluster sees no signal, test/replace the instrument cluster or its harness connector as per service procedures.
  8. After repair, clear codes, road test and re-scan to confirm B1368 does not return.
  9. Safety: disconnect battery before performing connector repairs and follow manufacturer procedures for handling electronic modules.

Likely causes

  • Wiring harness damage (chafing, rodent bite, pinched)
  • Loose or corroded connector at coil pack, ignition module, ECU or cluster
  • Failed ignition module/coils that generate the tach output
  • Open trace or component failure inside the instrument cluster
  • Blown supply fuse to cluster or ignition electronics

Fault status

⚠️ Status
Ignition system tachometer signal output circuit open — no tachometer (RPM) output detected on the expected circuit.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3.0 hours

Similar codes

B1367 B1369 B1273 U0113 U0073
89

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