U0253

Code

Generic U — Network/User

Lost Communication With Accessory Protocol Interface Module

Brand: Generic

Type: U — Network/User

Views: UK: 27 EN: 144 RU: 104

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

APIM (accessory protocol interface module) failure or software fault
Loss of module power or ground (blown fuse, poor ground, open power feed)
Damaged or corroded connector/pins at the APIM
CAN/LIN bus wiring fault (open, short to battery/ground, intermittent)
Missing or failed CAN bus termination resistor(s)
Module configuration or programming mismatch after replacement or update

Symptoms

Loss of infotainment, voice, or accessory functions controlled by APIM
One or more warning messages or inoperative controls on dash display
Intermittent features (Bluetooth, USB, phone, remote start) not working
Symptoms may be intermittent or permanent depending on fault
Other modules may report related U-codes or enter limp/limited modes

What to check

Read stored and pending DTCs and freeze frame with a professional scan tool
Attempt to communicate directly with the APIM using OEM-capable scan tool
Visually inspect APIM connector, pins and harness for corrosion, damage or water intrusion
Check fuses and relays supplying APIM power and accessory circuits
Measure APIM power and ground voltages with ignition in proper state
Measure CAN bus voltages and perform continuity/short checks

Signal parameters

CAN bus idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each to chassis)
CAN bus dominant: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (approximate differential ≈ 2.0 V)
Typical CAN differential voltage (dominant) ≈ 1.5–2.5 V
Typical CAN termination resistance ≈ 60 ohms between CAN_H and CAN_L (two 120 Ω in parallel)
Common CAN bit rates: 125 kbps, 250 kbps, 500 kbps (verify vehicle-specific rate)
APIM supply: nominal 12 V battery/ignition feed (verify voltage present and stable)

Diagnostic algorithm

Retrieve all network-related DTCs and freeze frame data. Note ignition state and voltage at time of fault.
Attempt to communicate with the APIM using a scan tool. If no communication, confirm the APIM does not respond on the bus.
Verify battery voltage and check fuses/relays for APIM power circuits; repair/replace as needed.
Verify APIM ground(s) have low resistance to chassis (
Visually inspect APIM connector and harness for damaged pins, corrosion, water intrusion, or repairs; repair connector/harness if needed.
With ignition on, backprobe APIM power and ground pins to confirm correct voltages under load.
Measure CAN_H and CAN_L voltages at the APIM connector with key on; confirm recessive ~2.5 V and proper dominant levels when active.
Check termination resistance across CAN_H and CAN_L with power off; expect ≈60 Ω. If open or incorrect, locate missing/failed terminator.
Perform short-to-power/ground checks on CAN lines and continuity back to other network modules; isolate segments as required.
If bus errors are present, remove or disconnect suspected aftermarket or recently added modules and retest.
If wiring and power/ground are good but no communication, attempt software reflash or known-good module swap if available to verify module failure before replacement.
Clear codes and road-test to confirm repair; monitor for reappearance of U0253 and related codes.

Likely causes

Blown fuse or poor battery/ignition power supply to APIM
Open or intermittent ground to the APIM
Corroded/damaged APIM connector or wiring harness
CAN high/low short to voltage or ground or to each other
Failed APIM hardware or corrupted software
Network bus 'bus-off' condition caused by a different failed module

Fault status

⚠️ Status

Lost Communication With Accessory Protocol Interface Module — APIM not responding on vehicle network; possible power, ground, wiring, termination, or module fault.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

Repair manuals