Code
U1706
ALFA ROMEO
U — Network/User
CAN bus communication between engine control module and ABS brake system
Views:
UK: 10
EN: 27
RU: 14
AI status
Completed
Completed
100%
Causes
- Damaged or corroded wiring or connector between ECM and ABS module
- Faulty ABS control module
- Faulty engine control module (ECM/PCM)
- Short to battery or ground on CAN_H or CAN_L
- Open circuit in CAN bus wiring or connectors
- Missing or failed CAN termination resistor(s)
Symptoms
- ABS warning lamp illuminated
- Brake/traction/ESP warning lights may also be on
- Malfunction Indicator Lamp (MIL) may set if ECM affected
- Loss of ABS functionality or intermittent ABS operation
- Loss of traction control or stability control features
- Possible limp-home behavior if ECM or ABS limits engine/driveability functions
What to check
- Connect a diagnostic scanner and retrieve U1706 plus any related U or C/P codes and freeze frame data
- Check vehicle battery voltage and charging system (stable >12.2 V at rest, >13.5 V running)
- Visually inspect ABS and ECM connectors for corrosion, bent pins, or water ingress
- Inspect CAN wiring harness for abrasions, pinched sections, or recent repairs
- Check for aftermarket devices tapped into the CAN bus (alarms, remotes) and remove/disable to test
- Measure CAN bus termination resistance across CAN_H and CAN_L (approx. 60 Ω with two 120 Ω terminations in parallel)
Signal parameters
- CAN physical layer (typical high-speed): CAN_H idle ≈ 2.5 V, CAN_L idle ≈ 2.5 V
- Dominant state differential voltage typically ≈ 1.5–2.5 V (CAN_H rises ~3.5 V, CAN_L falls ~1.5 V)
- Nominal bus bit rate commonly 250 kb/s to 500 kb/s on powertrain/ABS networks (verify OEM spec)
- Termination resistance across CAN_H and CAN_L ≈ 60 Ω (two 120 Ω terminators in parallel)
Diagnostic algorithm
- Record all stored codes and freeze frame data from ECM and ABS; note timestamps and related events
- Verify vehicle battery voltage and charging system; charge or maintain battery as needed
- Visually inspect ABS and ECM connectors and CAN harness routing; repair any damaged connectors or wiring
- Clear U1706 and related codes, then attempt to reproduce the fault while monitoring live data
- Measure CAN bus resistance between CAN_H and CAN_L with ignition off (expect ≈ 60 Ω); if open or shorted, isolate harness section and repair
- With ignition ON, measure DC voltage of CAN_H and CAN_L at both ABS and ECM connectors (compare to expected values); if abnormal, use an oscilloscope to view CAN waveforms for noise, missing recessive/dominant states, reflections or stuck bits
- If waveform shows errant node, isolate by disconnecting suspected modules (disconnect ABS module harness—follow manufacturer safety precautions) and observe if bus recovers; if bus returns to normal with a module disconnected, that module or its wiring is likely at fault
- Inspect and test grounds for ECM and ABS; clean and tighten ground points
- Check for aftermarket modules or devices connected to the bus; remove and retest
- If a module is replaced, follow OEM procedure for module programming/coding and then re-test to confirm communications restored
- After repair, clear codes and drive to verify no recurrence; re-scan for related stored codes
Likely causes
- Corroded or loose connector at ABS or ECM (common)
- Broken or chafed CAN pair wiring in harness routing (common)
- Failed ABS module (moderate likelihood)
- Short to power or ground on CAN lines (moderate likelihood)
- Missing/failed 120 Ω termination(s) or incorrectly fitted aftermarket device (less common)
- ECM hardware fault or corrupted software (less common)
Fault status
Status
CAN communication fault: ECM not receiving expected messages from ABS module. May be intermittent or continuous loss of CAN messages between these modules.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
U1706
FIAT
U — Network/User
CAN bus communication between engine control module and ABS brake system
Views:
UK: 8
EN: 24
RU: 15
AI status
Completed
Completed
100%
Causes
- Damaged or corroded wiring or connector between ECM and ABS module
- Faulty ABS control module
- Faulty engine control module (ECM/PCM)
- Short to battery or ground on CAN_H or CAN_L
- Open circuit in CAN bus wiring or connectors
- Missing or failed CAN termination resistor(s)
Symptoms
- ABS warning lamp illuminated
- Brake/traction/ESP warning lights may also be on
- Malfunction Indicator Lamp (MIL) may set if ECM affected
- Loss of ABS functionality or intermittent ABS operation
- Loss of traction control or stability control features
- Possible limp-home behavior if ECM or ABS limits engine/driveability functions
What to check
- Connect a diagnostic scanner and retrieve U1706 plus any related U or C/P codes and freeze frame data
- Check vehicle battery voltage and charging system (stable >12.2 V at rest, >13.5 V running)
- Visually inspect ABS and ECM connectors for corrosion, bent pins, or water ingress
- Inspect CAN wiring harness for abrasions, pinched sections, or recent repairs
- Check for aftermarket devices tapped into the CAN bus (alarms, remotes) and remove/disable to test
- Measure CAN bus termination resistance across CAN_H and CAN_L (approx. 60 Ω with two 120 Ω terminations in parallel)
Signal parameters
- CAN physical layer (typical high-speed): CAN_H idle ≈ 2.5 V, CAN_L idle ≈ 2.5 V
- Dominant state differential voltage typically ≈ 1.5–2.5 V (CAN_H rises ~3.5 V, CAN_L falls ~1.5 V)
- Nominal bus bit rate commonly 250 kb/s to 500 kb/s on powertrain/ABS networks (verify OEM spec)
- Termination resistance across CAN_H and CAN_L ≈ 60 Ω (two 120 Ω terminators in parallel)
Diagnostic algorithm
- Record all stored codes and freeze frame data from ECM and ABS; note timestamps and related events
- Verify vehicle battery voltage and charging system; charge or maintain battery as needed
- Visually inspect ABS and ECM connectors and CAN harness routing; repair any damaged connectors or wiring
- Clear U1706 and related codes, then attempt to reproduce the fault while monitoring live data
- Measure CAN bus resistance between CAN_H and CAN_L with ignition off (expect ≈ 60 Ω); if open or shorted, isolate harness section and repair
- With ignition ON, measure DC voltage of CAN_H and CAN_L at both ABS and ECM connectors (compare to expected values); if abnormal, use an oscilloscope to view CAN waveforms for noise, missing recessive/dominant states, reflections or stuck bits
- If waveform shows errant node, isolate by disconnecting suspected modules (disconnect ABS module harness—follow manufacturer safety precautions) and observe if bus recovers; if bus returns to normal with a module disconnected, that module or its wiring is likely at fault
- Inspect and test grounds for ECM and ABS; clean and tighten ground points
- Check for aftermarket modules or devices connected to the bus; remove and retest
- If a module is replaced, follow OEM procedure for module programming/coding and then re-test to confirm communications restored
- After repair, clear codes and drive to verify no recurrence; re-scan for related stored codes
Likely causes
- Corroded or loose connector at ABS or ECM (common)
- Broken or chafed CAN pair wiring in harness routing (common)
- Failed ABS module (moderate likelihood)
- Short to power or ground on CAN lines (moderate likelihood)
- Missing/failed 120 Ω termination(s) or incorrectly fitted aftermarket device (less common)
- ECM hardware fault or corrupted software (less common)
Fault status
Status
CAN communication fault: ECM not receiving expected messages from ABS module. May be intermittent or continuous loss of CAN messages between these modules.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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