U2050

Code

HUMMER U — Network/User

SIR PPS/CPS Communications Link malfunction

Brand: HUMMER

Type: U — Network/User

Views: UK: 9 EN: 16 RU: 10

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Page language: EN

Causes

Open or short in data bus wiring (CAN/LIN/serial) between PPS/CPS module and network
Poor electrical connection at module or gateway connectors (corrosion, loose pin, pushed-out terminal)
Blown fuse or loss of power/ground to the passenger sensing or SIR control modules
Failed passenger sensing module, SIR control module, or gateway/module on the bus
Intermittent wiring damage from chafing, water intrusion or previous repairs
Software/configuration mismatch or missing calibration in one or more modules

Symptoms

Malfunction Indicator Lamp(s) related to SIR/airbag or passenger sensing illuminated
Passenger airbag enable/disable status incorrect or unavailable
Stored U-codes and potentially related B-codes in other SIR or body modules
Possible loss of passenger presence/seat occupant detection or incorrect seat status
Vehicle may set other communication-related diagnostic trouble codes

What to check

Read all stored and pending DTCs and freeze frame data with a capable scan tool (prefer OEM/Tech 2/GS Tool). Note related U- and B-codes.
Check battery state-of-charge and system voltage; verify stable supply (12 V) during tests.
Inspect fuses and SIR circuit power/ground distribution related to passenger sensing and restraint modules.
Visually inspect wiring harnesses, connectors and pin terminals at the passenger presence module, SIR module, and gateway for corrosion, bending, or pushed-out pins.
Check for other modules reporting U-codes on the same bus to determine scope of the communication issue.
With key on, use scan tool or oscilloscope to verify bus activity and message presence for passenger sensing nodes.

Signal parameters

Typical high-speed CAN idle (recessive) voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both referenced to battery ground) — note dominant state shifts CAN_H higher (~3.5 V) and CAN_L lower (~1.5 V).
Termination: two 120 Ω resistors in parallel → ~60 Ω measured across CAN_H to CAN_L (typical for high-speed CAN).
Message frequency: passenger presence module messages are periodic; verify expected message IDs and intervals with OEM data (scan tool).
LIN or single-wire communication (if used on some vehicles) will show a resting voltage near battery and pulsed low to signal — verify with OEM documentation and oscilloscope.

Diagnostic algorithm

Connect an appropriate OEM-capable scan tool, record all U- and related B/C/P codes and freeze frame data. Note when fault first occurred and any intermittent history.
Verify battery voltage >12.4 V (or manufacturer-specified) during diagnosis. Charge or stabilize battery if low before further testing.
Visually inspect wiring and connectors at passenger presence module, SIR/airbag control module, instrument cluster/gateway and any intermediate connector points for damage, corrosion, bent pins or water intrusion.
Check SIR-related fuses and module power/ground circuits for continuity and correct voltages. Repair any low/absent power or ground before continuing.
Using the scan tool, check for presence of passenger sensing messages on the bus. If tool supports it, monitor message IDs, frequency, and payload. Note whether the module is listed as 'not responding.'
If bus messages are absent or corrupted, use a digital multimeter and/or scope to measure CAN_H and CAN_L at the module connector and at gateway/ECM connectors: verify idle voltages and dominance behavior while exercising the bus. Measure resistance across CAN_H to CAN_L with power off to confirm ~60 Ω termination.
If wiring is suspected, perform continuity tests between module connector and gateway/ECM; check for shorts to battery and ground. Wiggle test harness while monitoring live data to expose intermittent faults.
Repair harness/connectors or restore proper termination/power/ground as found. Replace damaged connector pins or sections of wiring; apply corrosion protection.
If wiring and power are good but the module does not communicate, follow OEM procedures to reprogram/configure or replace the passenger sensing or SIR module. After any module replacement, perform required programming and system configuration per service information.
Clear codes, re-test system operation, and verify no reoccurrence of U2050 and that passenger sensing messages are present and valid. Road test if necessary to confirm permanent repair.
Safety note: Always follow manufacturer SIR/airbag disabling procedures (battery disconnect and specified wait time) before disconnecting or servicing airbag or passenger sensing connectors to avoid accidental deployment.

Likely causes

Damaged connector or pin at passenger presence or SIR module
Short to battery or ground on the communication line
Defective passenger sensing module or SIR ECU
Open termination (missing 60 Ω equivalent) or multiple termination faults on the CAN bus
Low battery voltage or weak battery causing communication errors

Fault status

⚠️ Status

Communication fault on SIR PPS/CPS link — passenger sensing/child presence module messages missing or corrupted. Possible open/short on data bus, connector/power/ground issue, or module failure.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 2.5 hours

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