CAT Engine 5466 Fault Code: Ether Hold Relay short to +batt
Also called Ether Hold Relay Short to +Batt, Ether Hold Relay short to +Batt
Ether Hold Relay short to +batt · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 5466 means the ECM has detected a short circuit to +Battery at the output to the ether hold relay, after being powered up for at least two seconds. Ether injection is disabled when this code is active, and the engine may be difficult to start in cold weather.
Medium severity. The engine will still run and drive normally, but cold-weather starting aid is disabled. In cold climates this can turn into a real no-start or hard-start problem, so it should not be ignored for long, especially heading into cold weather.
What does CAT Engine error code 5466 mean?
Code 5466 is set by the Electronic Control Module (ECM) when it detects a short circuit to +Battery voltage at the output wire that drives the ether hold relay. The ECM checks for this condition after it has been powered up for two seconds, and in one version of the logic, it can only detect the fault when the ether hold relay is actually energized.
The ether system helps start diesel engines in cold weather by injecting ether into the intake. It has two driver outputs from the ECM: one drives the ether start relay with +Battery voltage to fire the ether solenoid, and the second drives the ether hold relay, which keeps the solenoid energized afterward at a reduced voltage through a dropping resistor and diode assembly instead of full battery voltage. That reduced-voltage hold stage exists because the solenoid will be damaged if full battery voltage is applied to it continuously.
When the ECM sees a short to +Battery on the hold relay output, it cannot safely control that reduced-voltage hold circuit, so it shuts down ether injection entirely to protect the solenoid and the circuit. The trade-off is that starting aid is no longer available, which matters most in cold conditions.
What triggers a CAT Engine 5466 code?
The ECM sets this code once it has been powered up for at least two seconds and detects a short circuit to +Battery at the ether hold relay output. In one logic version, this detection can only happen while the ether hold relay is energized. A related version of the logic also watches for an open circuit at the same output, in addition to the short to +Battery.
Common causes of 5466
- Damaged, corroded, or chafed connectors and/or wiring in the ether hold relay circuit
- A general problem in the wiring harness carrying the hold relay signal
- Ether canister is empty, which can affect system behavior and fault detection
- Ether solenoid is faulty or needs replacement
- The resistor and diode assembly used for the reduced-voltage hold stage needs replacement
- Faulty or malfunctioning starting aid switch
- Intermittent electrical problem in the circuit
- Faulty ECM
How to troubleshoot CAT Engine 5466: first checks
- With the machine safely shut down and battery disconnect off if possible, inspect all connectors in the ether system wiring for corrosion, moisture, or damage, and check for chafed or pinched wiring along the harness routing
- Check the ether canister level. An empty canister is listed as a possible cause and is a quick, no-tool check
- Inspect the starting aid switch for proper operation, sticking, or failure to return to its normal position
- Check the ether solenoid and the resistor/diode dropping assembly for visible damage or signs of overheating, since the hold circuit relies on reduced voltage through this assembly
- Use a diagnostic scan tool to confirm the active code and check for related stored codes before disturbing wiring, so you have a baseline
- If wiring, connectors, canister, switch, solenoid, and resistor/diode assembly all check out, consider the ECM output driver itself as a possible cause
How the code clears
No separate clearing step is listed for this code beyond correcting the underlying short circuit or faulty component. Once the wiring, connector, solenoid, resistor/diode assembly, starting aid switch, or canister issue is repaired, the code should stop being logged on the next power-up cycle where the ECM checks the circuit. If the fault is intermittent, it may take more than one key cycle or cold start attempt to confirm the repair.
Frequently asked questions
What does CAT code 5466 mean?
It means the ECM has detected a short circuit to +Battery voltage at the output wire that drives the ether hold relay, after being powered up for at least two seconds. Ether injection is disabled as a result.
Will my engine still start with code 5466 active?
Yes, the engine can still be started normally in most conditions, but the ether starting aid is disabled, so cold starts may be harder. The engine may be difficult to start, especially in cold temperatures where ether injection would normally help.
Can an empty ether canister cause this code?
Yes, an empty ether canister is listed as one of the possible causes across multiple versions of this diagnostic logic, so it is worth checking early since it takes no tools.
Is this an electrical problem or a solenoid problem?
It can be either. Possible causes include damaged wiring and connectors, a faulty ether solenoid, a bad resistor and diode dropping assembly, a faulty starting aid switch, or in some cases a faulty ECM. Careful inspection is needed to isolate which one it is.
Why does the ether system use a hold relay at reduced voltage instead of full battery voltage?
Because the solenoid will be damaged if full battery voltage is applied to it continuously. The hold relay uses a dropping resistor and diode assembly to reduce voltage after the initial start pulse, protecting the solenoid.
Does this code affect engine rpm or coolant temperature limits?
Not directly, but normal ether system operation depends on those values. AUTO ether injection normally runs for a minimum of 10 seconds at 10 °C (50 °F) up to a maximum of 130 seconds at -40 °C (-40 °F), and is disabled above 1900 RPM or above 10 °C (50 °F) coolant temperature. When code 5466 is active, none of this matters since ether injection is disabled entirely.
Is code 5466 urgent to fix?
It is not an emergency for engine operation, but it should be diagnosed within the shift, especially before cold weather, since a hard-starting engine in freezing conditions can strand equipment or drain batteries during repeated crank attempts.