CAN Bus Link Lost Between WS Controller and Engine ECM

Common Symptoms

• WS Controller LCD on the side panel displays E070 and unit shuts down or refuses to start
• Engine hour meter, RPM, and coolant temperature readings disappear from the WS Controller display
• No engine fault codes appear on the WS Controller even though the engine may have its own active DTCs
• Unit may crank but immediately trip off-load with E070 on the panel
• Yellow or red fault indicator light on the controller panel stays solid after attempting RUN
• Engine OEM diagnostic tool (JD Service Advisor, CAT ET, or Cummins INSITE) may still communicate with the ECM independently, confirming the problem is the link, not the ECM itself
• Pressing STOP and returning to AUTO does not clear the fault, it comes back every start attempt

Probable Causes (Ranked by Likelihood)

• Damaged, corroded, or unplugged J1939 CAN harness connector at the WS Controller or engine ECM end Very Likely
• Broken, chafed, or shorted CAN High or CAN Low wiring between the WS Controller and the engine ECM Very Likely
• Missing or failed 120-ohm CAN bus termination resistor at one or both ends of the J1939 network Likely
• Engine ECM or ECU has lost power or ground, taking the CAN node offline Likely
• WS Controller internal CAN transceiver failure or controller firmware fault Possible
• Engine ECM locked up or in a fault state that drops it off the J1939 network Possible
• Incorrect J1939 address configuration after a controller or ECM replacement Less Likely

Step-by-Step Diagnostic Procedure

1. Start with a visual check. Open the control panel enclosure and trace the J1939 CAN harness from the WS Controller to the engine ECM. Look for connectors that are loose, unplugged, or corroded. Push each connector fully home and check for bent pins. This alone fixes E070 more often than anything else on rental units that get bounced around on job sites.

2. Check ECM power and ground first. Measure DC voltage at the engine ECM power supply pins with the key switch in RUN. You need at least 11.5V DC on a 12V system or 23V DC on a 24V system. A weak or open ground at the ECM will drop the entire CAN node off the network. Clean and retorque any ECM ground straps you find.

3. Measure CAN bus resistance. With the unit fully powered OFF and both the WS Controller and the engine ECM disconnected from the harness, put your multimeter across the CAN High and CAN Low wires at the middle of the harness. You should read 60 ohms, which is two 120-ohm termination resistors in parallel. A reading near 120 ohms means one resistor is missing or open. A reading near zero ohms means the wires are shorted together. Either condition will cause E070.

4. Check each termination resistor individually. There is one 120-ohm resistor at the WS Controller end of the CAN network and one at the far engine ECM end. Disconnect each connector and measure resistance across the CAN High and CAN Low pins at each device. Each should read 120 ohms on its own. Replace any resistor that reads open (OL) or far out of spec.

5. Inspect the full CAN harness run for damage. Follow the harness from the controller box along its routing to the engine compartment. Look for spots where the jacket has rubbed through against the frame, pinch points at panel edges, and heat damage near the exhaust. A chafed wire that shorts CAN High to CAN Low or to chassis ground will pull the whole network down.

6. Try communicating with the engine ECM directly using the engine OEM tool. Connect JD Service Advisor, CAT ET, or Cummins INSITE via the engine diagnostic port. If the OEM tool connects and reads the ECM successfully, the ECM itself is fine and the fault is in the harness or the WS Controller side. If the OEM tool also cannot connect, the ECM has lost power or ground, or the ECM has internally failed.

7. If wiring and connectors all check out, cycle power to the WS Controller completely. Turn the unit OFF, wait 60 seconds, and restart. A one-time controller firmware glitch can latch E070 without a real hardware fault. If E070 returns within seconds of restart every time, and all wiring is confirmed good, the WS Controller itself may have a failed CAN transceiver and will need to be replaced or sent to Sullair for evaluation. This step requires a Sullair service rep or advanced tech.

Frequently Asked Questions