U0089

Code

Generic U — Network/User

Vehicle Communication Bus G

Brand: Generic

Type: U — Network/User

Views: UK: 20 EN: 41 RU: 21

AI status

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Page language: EN

Causes

Open or short in Bus G wiring (CAN/LIN/FlexRay depending on vehicle)
Faulty or unpowered control module on Bus G
Damaged or corroded connector or pin
Missing or incorrect termination resistor(s) on the bus
Low battery or poor ground affecting module communications
ECU software/firmware mismatch or module addressing fault

Symptoms

One or more modules not detected by scan tool on Bus G
Multiple warning lights or messages related to affected systems
Loss of operation for systems controlled by modules on Bus G (e.g., ABS, HVAC, instrument cluster)
Intermittent faults or systems that work sporadically
MIL on and stored U0089 code(s)

What to check

Verify vehicle battery voltage and battery ground connections are within specification
Scan vehicle with OEM-level scan tool: read modules present/absent, freeze frame data, and related U-codes
Visually inspect wiring and connectors along Bus G for damage, corrosion, or loose connections
Check fuses and power/ignition feeds to modules on Bus G
Perform a wiggle test on harness while monitoring communications for intermittent changes
Measure bus termination resistance (expected ~60 ohms for single CAN bus with two 120 Ω terminators in parallel)

Signal parameters

Nominal CAN idle voltages (single-wire CAN not excluded): CAN_H ≈ 2.5–3.5 V, CAN_L ≈ 1.5–2.5 V (recessive ~2.5 V each). Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V, differential ≈ 2.0 V
Expected differential impedance across bus termination ≈ 60 Ω (two 120 Ω terminators in parallel)
No short to battery or ground on either bus line (line-to-Vb and line-to-ground should be high resistance)
LIN idle: near battery voltage through pull-up (if Bus G is LIN on some architectures)

Diagnostic algorithm

Confirm U0089 is current or historical; record freeze-frame and related codes.
Check for technical service bulletins (TSBs) or software updates related to Bus G communications.
Verify battery voltage >12 V and good ground connections; repair as required.
Using scan tool, list modules found on network and note which expected modules are missing on Bus G.
Visually inspect connectors and wiring of modules on Bus G; repair obvious damage and reseat connectors.
Check power and ground at the unresponsive module(s) (key on) — verify proper supply voltages and ground integrity.
Measure resistance between Bus G high and low with ignition off; expect ~60 Ω. If open or short, isolate segments by disconnecting modules until normal termination value is found.
With key on, measure DC voltages on Bus G lines at a module connector. Compare to expected ranges. If voltages out of range, inspect for short to battery/ground or missing termination.
If DMM checks OK, view waveforms with oscilloscope during cranking/idle to confirm clean differential signals and identify noise/reflections.
Disconnect suspected faulty module(s) and re-check bus behavior. If bus returns to normal with module disconnected, suspect that module for replacement or repair.
If wiring fault is found, repair harness per OEM splice/repair procedures and protect against recurrence.
After repair or module replacement, clear codes, perform relearns or programming if required, then verify by driving and rescanning to ensure U0089 does not return.