P1637

Code

Other P — Powertrain

Can Link ECM/ABSCM Circuit / Network Malfunction

Brand: Other

Type: P — Powertrain

Views: UK: 45 EN: 154 RU: 50

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Page language: EN

Causes

Open or shorted CAN bus wiring (CAN H/CAN L) between ECM and ABSCM
Faulty or corroded connector(s) at ECM, ABSCM, or intermediate junctions
Failed ECM, ABSCM, or another node causing bus errors
Missing or low module power/ground affecting CAN transceiver operation
Improper/missing CAN bus termination (faulty/missing resistors)
Intermittent wiring fault (chafing, pinched wire) or water intrusion

Symptoms

Illuminated ABS warning lamp and/or CEL/MIL
Loss of ABS function or degraded braking features
Intermittent or continuous communication-related codes present
Multiple modules reporting lost-communication or network-related codes
Occasional no-start or drivability issues if ECM communication affected

What to check

Retrieve freeze frame and full scan tool data; note all communication/network codes and timestamps
Check vehicle battery voltage and charging system; low battery can cause communication faults
Visually inspect wiring harnesses and connectors at ECM, ABSCM and junctions for corrosion, damage, or water intrusion
With ignition ON, check for proper power and ground at ECM and ABSCM (reference factory pinouts)
Using a scan tool, confirm whether both ECM and ABSCM are present on the network and responding
Inspect CAN termination resistors (measure resistance between CAN H and CAN L with power off)

Signal parameters

CAN bus idle voltages: CAN_H ≈ 2.5–3.5 V, CAN_L ≈ 1.5–2.5 V (each referenced to chassis ground)
Differential idle voltage (CAN_H − CAN_L) ≈ 0 V with both at ~2.5 V; dominant state drives differential ~2 V
Typical CAN bit rates: 125 kbps / 250 kbps / 500 kbps depending on vehicle (verify factory spec)
Bus termination resistance ≈ 60 Ω (two 120 Ω terminators in parallel) between CAN_H and CAN_L (power off)
Message frequency: ECM and ABSCM should transmit periodic messages — verify presence with a capable scan tool or oscilloscope

Diagnostic algorithm

Connect a capable diagnostic scan tool and read all DTCs and module presence. Record codes and freeze frame. Note whether ECM and ABSCM appear on the tool. 2) Verify battery voltage (12.4–12.8 V at rest) and system charging. Low battery can produce network faults. 3) Visually inspect connectors and wiring at ECM, ABSCM, and any intermediate splice/junctions. Repair any corrosion or damage. 4) With ignition ON (engine off), measure supply voltage and ground at ECM and ABSCM power/ground pins. Repair any open circuits. 5) With power off, measure resistance between CAN_H and CAN_L at a convenient connector; expect ≈ 60 Ω. If open or shorted to ground/power, isolate and repair. 6) With vehicle ignition ON, use a scope or quality CAN bus analyzer to view CAN_H and CAN_L waveforms at multiple points (near ECM and ABSCM). Look for proper recessive levels, dominant pulses, reflections, or large noise. 7) If a wiring fault is suspected, perform continuity checks between modules for CAN_H and CAN_L, and check for shorts to battery, ground, or chassis. 8) Perform wiggle tests on harness while monitoring bus for errors to find intermittent faults. 9) If one module appears silent or corrupts the bus, isolate by disconnecting the suspected module (if safe and per service info) and observe whether communication returns. 10) If wiring and power/grounds are good and the network still fails, consider replacing or bench-testing the suspected module(s) per manufacturer instructions. 11) After repairs, clear codes and perform a road test to confirm the fault does not return and that all modules are present and communicating.

Likely causes

Damaged CAN H or CAN L conductor between ECM and ABSCM
Corroded pin or loose connector at one of the modules
Failed CAN transceiver in ECM or ABSCM
Loss of module supply voltage or ground resulting in a silent node
Bad termination resistor (open or shorted), causing reflections and errors

Fault status

⚠️ Status

CAN link ECM/ABSCM circuit/network malfunction — communication between Engine Control Module and ABS Control Module is unreliable or absent. Check CAN bus physical layer, module power/ground, connectors, and module integrity.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours