JCB P0321-87 – Engine ECU: Missing Engine Speed CAN Message

The system has detected a CAN bus message error related to the engine speed signal from the Engine ECU. The '-87' suffix denotes a 'Missing message' failure type, meaning a receiving module (such as the transmission, hydraulic, or main vehicle controller) expected to see the engine speed signal on the network but did not. This indicates a communication issue between the Engine ECU and the receiving system, or a failure of the crankshaft position sensor failing to provide the initial speed signal to the ECU.

• JS130
• JS200
• JS230
• JS330
• 3CX
• 4CX
• JS Series Excavators
• Backhoes
• Telehandlers
• Wheel Loaders

1. 1

   Visually inspect wiring harnesses (especially the main engine harness and ECU interconnects) for chafing, rubbing, melting, or corrosion.

2. 2

   Inspect main connectors on the Engine ECU, crankshaft position sensor, and CAN bus junctions for bent pins, corrosion ('green death'), moisture, or debris.

3. 3

   Verify all machine earth connections are clean and tight, and check battery voltage and terminal condition.

4. 4

   Measure CAN bus termination resistance with power off (should be approximately 60 Ohms between CAN_H and CAN_L; 120 Ohms indicates a missing resistor or open circuit, and near 0 Ohms indicates a short circuit between CAN_H and CAN_L).

5. 5

   Measure CAN bus voltages with ignition ON (CAN_H should be 2.5V-3.0V, CAN_L should be 2.0V-2.5V).

6. 6

   Check for shorts to ground on CAN_H and CAN_L lines with power OFF (should read as an open circuit or Mega-ohms).

1. 1

   Repair wiring and connectors

   If visual inspection reveals damaged wiring, shorted/open circuits, or corroded pins, clean with electrical contact cleaner and repair the harness sections. Replace the harness if it cannot be reliably repaired.

2. 2

   Test and replace engine speed sensor

   If the code is caused by a lack of initial signal, test the crankshaft position sensor. A two-wire magnetic pickup should show 750-2,000 Ohms resistance and output approximately 0.5V AC while cranking. Replace if out of specification.

3. 3

   Restore CAN termination

   If CAN resistance measured 120 Ohms, locate the missing or faulty terminating resistor (often in the engine harness) and replace it to restore the 60 Ohm network resistance.

4. 4

   Isolate faulty modules

   If wiring and sensors are good, systematically disconnect one module at a time (e.g., transmission controller, display panel) and re-check CAN resistance and voltages to identify if a single ECU is bringing down the network.

5. 5

   Replace Engine ECU

   If all other components and wiring are verified good, the Engine ECU may have a faulty CAN transceiver. Replace the Engine ECU.

6. 6

   Clear codes and verify

   Reconnect the battery, turn the ignition on, clear fault codes using the JCB Service Master tool, and operate the machine through a full duty cycle to ensure the code does not return.