P1794 on Mazda: How to Diagnose & Fix
Capacitor (i-ELOOP) System Malfunction
1 Mazda model · 1 documented issue · $600-$1,800 repair
P1794 on Mazda by model: symptoms, diagnosis and fix
On i-ELOOP equipped BM/BN Mazda3s, regenerative braking energy is stored in an electric double-layer capacitor mounted in the engine bay and fed back to the 12V system through a DC-DC converter. The capacitor develops an internal open circuit, or the DC-DC converter fails, and the PCM sets P1794 with an 'i-ELOOP Malfunction' message in the instrument cluster plus the master warning and battery/charging lights. Because the DC-DC converter also supplies the 12V system when i-ELOOP is active, a failure can leave the alternator carrying everything, run the battery down and disable i-stop. Mazda also issued a service bulletin for false i-ELOOP faults triggered when the accessory belt gets wet in heavy rain or deep water, so a wet-weather-only warning is not necessarily a dead capacitor.
Common Symptoms
- 'i-ELOOP Malfunction' message in the instrument cluster
- Charging system / battery warning light on
- Master warning light illuminated
- i-stop stops working
- Repeated dead or weak 12V battery
How to Fix
Pull the exact DTC and sub-code first. If the fault only appears in heavy rain or after driving through water, check for the applicable PCM reprogramming bulletin and inspect the accessory belt and pulleys for slip before condemning hardware. For a hard, repeatable fault, test the capacitor unit and the DC-DC converter separately - the capacitor assembly and the converter are separate parts and shops frequently replace the wrong one. Also verify the 12V battery and grounds, since a weak battery can mimic i-ELOOP faults and disable i-stop.
Sources for this issue (4)
P1794 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P1794 mean on a Mazda?
P1794 stands for "Capacitor (i-ELOOP) System Malfunction." The PCM monitors the i-ELOOP electric double-layer capacitor and the DC-DC converter that steps its stored voltage down to the 12-volt system. P1794 sets when the capacitor circuit does not charge, discharge, or report correctly - most commonly an open or high-resistance path in the signal harness between the DC-DC converter and the capacitor. Mazda documented that an oxide film can form on the terminals of that signal-harness connector, which is a key root cause of this code. On Mazda it is documented across 1 model: Mazda3.
What are the most common causes of P1794?
The most common causes of P1794 are: Oxide film on the signal-harness connector terminals between the DC-DC converter and the capacitor (Mazda-documented cause), Failed i-ELOOP capacitor assembly with an internal open circuit, Failed DC-DC converter, Open or damaged wiring between the capacitor, DC-DC converter, and alternator, Poor ground or corroded connector terminals. The specific cause varies by vehicle.
How much does it cost to fix P1794 on a Mazda?
Published repair estimates on Mazda range from $600 to $1,800 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P1794 on a different make?
View P1794 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.