P1621

Code

DS P — Powertrain

Inside ECU (CAN)

Brand: DS

Type: P — Powertrain

Views: UK: 1 EN: 3 RU: 2

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Page language: EN

Causes

Faulty ECU CAN transceiver or internal ECU hardware failure
Open, shorted or intermittent CAN_H or CAN_L wiring
Poor or missing ECU power or ground supply
Corroded or loose connectors at the ECU or along the CAN bus
Incorrect termination (missing or damaged 120 Ω resistors)
Vehicle software/firmware error or incompatible module programming

Symptoms

Malfunction indicator lamp (MIL) or dashboard warning related to communication
Loss or intermittent operation of functions controlled via CAN (instruments, immobilizer, body modules)
Multiple communication-related DTCs present (U-codes or other manufacturer codes)
Vehicle may enter limp or reduced functionality mode for affected systems
Intermittent faults that disappear after key cycle or battery disconnect

What to check

Read all stored and pending codes and freeze frame data; record occurrences and related U-codes
Check vehicle battery voltage and condition; verify stable supply (12.0–14.5 V) with key on
Inspect ECU and CAN-bus connectors for corrosion, bent pins, water ingress or damage
Verify fuses and power/ground circuits to the ECU (measure actual voltages at ECU connector)
Measure CAN bus termination resistance with ignition off (expected ~60 Ω between CAN_H and CAN_L)
Measure CAN_H and CAN_L voltages with key ON, engine OFF (see signal parameters)

Signal parameters

CAN bus idle (recessive) single-ended: 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 V)
Termination resistance (power off): approx. 60 Ω between CAN_H and CAN_L (two 120 Ω terminators in parallel)
Expected data rates vary by vehicle (commonly 125 kbps, 250 kbps, 500 kbps); verify vehicle-specific rate
No valid CAN frames or excessive error frames visible on the oscilloscope indicate bus or node fault

Diagnostic algorithm

Capture and save all DTCs (including U-codes) and freeze frame; note when code sets and any patterns.
Check battery state and ensure stable supply. Charge or replace battery if voltage unstable.
Visually inspect ECU connector and harness for damage, moisture, or corrosion; repair any damaged wiring or pins.
With ignition off, measure termination resistance between CAN_H and CAN_L at a convenient harness connector; expect ~60 Ω. If abnormal, locate and repair open or shorted terminators.
With ignition ON (engine OFF), measure CAN_H and CAN_L voltages at the ECU connector; compare to expected signal parameters. A line stuck high/low indicates short or internal transceiver fault.
Use an oscilloscope or high-quality scan tool to monitor CAN frames while exercising affected systems. Look for missing frames, repeated error frames, or excessive noise.
Isolate the fault by disconnecting non-essential CAN nodes (one at a time) to see if the error clears; this helps locate a shorting module or damaged section of harness.
Verify ECU supply and ground pins for correct voltages and continuity to chassis ground. Repair any supply/ground issues before replacing modules.
Check for manufacturer technical bulletins or required software updates; reprogram or update ECU if advised by the manufacturer.
If wiring, connectors, terminators and power/ground are verified good and the fault persists, consider ECU internal failure. Replace or repair ECU only after confirming external bus integrity and following manufacturer procedures for coding/programming.
After repair, clear codes and perform full functional test and road test to confirm repair; monitor for code return.

Likely causes

Damaged or corroded ECU connector pins causing intermittent CAN signals
Loss of ECU supply voltage or poor ground causing internal transceiver faults
Short to battery or ground on CAN_H or CAN_L near the ECU
Failed ECU CAN transceiver (internal component fault)
Missing/failed termination resistor (one of the 120 Ω terminators open)
Recent module replacement or software update left ECU unprogrammed or incompatible

Fault status

⚠️ Status

Internal ECU CAN communication fault detected. Possible causes include ECU transceiver failure, wiring/connector faults on the CAN bus, missing termination or power/ground issues. Verify bus integrity and ECU supplies before replacement.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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P1621 — Inside ECU (CAN)