U0689

Code

Generic U — Network/User

Lost Communication With Turbocharger/Supercharger B Temperature Sensor

Brand: Generic

Type: U — Network/User

Views: UK: 34 EN: 43 RU: 33

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or shorted sensor wiring (signal, reference, or ground)
Corroded, damaged, or loose connector at the sensor or control module
Failed turbocharger/supercharger B temperature sensor (NTC or electronic)
Faulty control module or module software/firmware issue
CAN/LIN bus communication fault or high network bus error rate
Water intrusion, oil contamination, or physical damage at sensor

Symptoms

Malfunction Indicator Lamp (MIL) or warning light illuminated
Reduced engine power or limp-home mode (boost control may be limited)
Erratic boost behavior or turbocharger control faults
Poor drivability or reduced fuel economy
No temperature reading or implausible temperature values for turbocharger B in live data

What to check

Retrieve freeze frame and full DTC list; note related codes and network errors
Visually inspect sensor harness, connector, and turbocharger area for contamination or damage
Use a scan tool to view live data for turbocharger B temperature and compare to turbocharger A (if present)
Backprobe connector to check reference voltage, signal voltage, and ground at key operating temperatures
Check wiring continuity and resistance between sensor and control module; wiggle harness while monitoring data
Inspect CAN/LIN bus health and check for other modules reporting communication errors

Signal parameters

Sensor type: typically an NTC thermistor (resistance decreases as temperature rises) or an electronic temperature sensor
Typical signal voltage range: approx. 0.5–4.5 V (varies by manufacturer) mapped to ambient to high turbo temps
Typical temperature measurement range: roughly -40°C to +150°C (system-dependent)
Resistance at ambient: commonly in the kilohm range; resistance should change smoothly when sensor is heated/cooled
Communication: sensor provides analog voltage to PCM or communicates over local bus (LIN/CAN) on some systems

Diagnostic algorithm

Connect a capable scan tool. Record U0689 and any related codes. Check freeze frame and live data for turbocharger B temperature.
Perform a visual inspection of the turbocharger B area: look for damaged harness, oil/water ingress, crushed or exposed wires, and connector corrosion.
With ignition ON (engine off) backprobe the sensor connector: verify reference voltage (if used), signal voltage, and ground presence per vehicle service data.
With the engine running/warmed, monitor the temperature reading for sensor B while comparing to sensor A (if present). If sensor B shows no change or implausible values while A behaves normally, suspect sensor or wiring to B.
Check continuity and resistance of the sensor circuit between the sensor connector and the control module harness connector. Repair any opens, shorts to ground, or shorts to voltage found.
If the sensor is a passive thermistor, disconnect it and measure resistance as the sensor is warmed/cooled to confirm resistance changes smoothly. Replace sensor if resistance is out of expected pattern or specification.
If sensor signals are correct at the connector but the module still reports lost communication, inspect module connector pins and wiring at the module. Check for CAN/LIN network errors and repair bus faults.
If wiring and sensor check good, consider module software updates or module replacement only after confirming no wiring or connector faults and consulting manufacturer procedures.
Clear codes and perform a road or operational test to verify the fault does not return. Document findings and repairs.

Likely causes

Damaged/loose connector at the sensor (most common)
Broken or chafed wiring harness between sensor and module
Sensor failure due to heat/oil exposure
Intermittent wiring short to voltage/ground or open circuit
Module side connector or module fault (less common)

Fault status

⚠️ Status

Lost Communication With Turbocharger/Supercharger B Temperature Sensor — control module not receiving valid temperature data from the turbocharger/supercharger B sensor; may be intermittent or permanent until repaired.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours