Code
P1622
CITROEN
P — Powertrain
Inside ECU (CAN)
AI status
Completed
Completed
100%
Causes
- Lost or intermittent CAN bus communication between Inside ECU and network
- Damaged or corroded connectors or wiring on CAN H/L, power or ground to the Inside ECU
- Blown fuse or missing supply/ignition feed to the Inside ECU
- Failed CAN transceiver in the Inside ECU
- Battery low or poor battery connection causing modules to drop off the bus
- Faulty or incompatible replacement Inside ECU (incorrect programming)
Symptoms
- MIL (check engine) or communication lamp may be stored/illuminated
- Loss or intermittent operation of functions controlled by Inside ECU (interior lighting, central locking, interior switches, cabin functions)
- Other modules reporting network errors or loss of multiple modules in scan tool
- Intermittent or permanent no-response when querying Inside ECU with diagnostic tool
- Possible erratic behavior of multiple body electronics
What to check
- Read all stored DTCs and freeze frame data from all modules — note which modules report CAN errors
- Use a capable scan tool to poll the Inside ECU and confirm it appears (or is missing) on the CAN network
- Check battery voltage and health; ensure stable supply (13.0–14.5 V) during tests
- Inspect fuses and relays related to interior/comfort modules and power supply to Inside ECU
- Visually inspect Inside ECU connector for corrosion, bent pins, water ingress, or broken wires
- Perform a wiggle/connector-press test while monitoring network for intermittent codes or module appearance
Signal parameters
- CAN bus idle single-ended voltages (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V
- CAN bus dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
- Bus termination: two 120 Ω resistors in parallel gives ≈ 60 Ω between CAN_H and CAN_L when vehicle off/terminated
- Typical CAN data traffic: modules should respond to diagnostic requests and broadcast periodic messages — scan tool will show module presence/response rates
Diagnostic algorithm
- Confirm vehicle battery is charged and connections are clean/tight. Re-test after charging if low voltage was present.
- Read and record all codes from all modules. Note any U- or P-codes indicating network issues.
- Use a scan tool to confirm whether the Inside ECU is present on the bus and whether it responds to requests. Attempt to read module identity and software level.
- Check fuses/power/ground for the Inside ECU; verify supply voltages at the ECU connector with ignition on and engine off as per wiring diagram.
- Visually inspect the Inside ECU connector and wiring harness for damage, corrosion, water ingress, or rodent damage. Repair any wiring defects.
- With ignition on, measure CAN_H and CAN_L voltages at the Inside ECU connector and at another known-good CAN node. Compare to expected values and look for large imbalance, shorts, or stuck levels.
- With vehicle power off, measure resistance between CAN_H and CAN_L to confirm ≈60 Ω termination. Disconnect modules as needed to isolate a short or open.
- If a short or open is isolated to wiring, repair and retest. If wiring and power/ground are good and the module does not respond, consider ECU internal fault or faulty transceiver.
- Check for manufacturer technical service bulletins (TSBs) or required reprogramming; if ECU replacement is required ensure proper programming and matching part number/flash level.
- After repairs, clear codes and perform functional test and road test; verify codes do not return and module stays on the CAN network.
Likely causes
- Open or shorted CAN H/L wiring at interior ECU connector
- Corroded pin or poor ground at Inside ECU
- Blown fuse supplying ECU power or ignition feed removed
- Failed CAN transceiver inside the Inside ECU
- Module asleep or not initialized after battery disconnect or replacement
Fault status
Status
Interior ECU not communicating on CAN bus — messages missing or no response from Inside ECU (CAN communication fault).
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email