P23D3: Cylinder 1 Fuel Heater Control Circuit Low

P23D3 reports that the control circuit of the cylinder 1 fuel heater is pulled toward ground. It follows the high code P23D2 in the numbering, not the other way round. A ground short on a heater path rated at a few hundred watts lets far too much current flow, so the heater unit or a fuse cuts the channel and cylinder 1 starts with cold fuel while the other heaters still work. Bosch states that its Flexstart unit detects shorts on its four heat circuits individually and reports them to the engine module. No manufacturer documents P23D3 publicly. CARB demands circuit checks on heated fuel preparation outputs. Expect a one-cylinder stumble on cold ethanol starts and possibly a blown fuse. Open circuit is P23D1, the other cylinders follow from P23D7.

Low severity. Can I keep driving?You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.

Cylinder 1 is numbered according to the manufacturer: check your engine's manual before working on it.

Symptoms

Single-cylinder misfire on cold ethanol starts
Blown fuse in the fuel heater circuit
Engine warning lamp, depending on manufacturer

Most likely causes

Cylinder 1 heater wire chafed to ground on the intake or engine
Heater at cylinder 1 shorted to its housing
Fuel or water in the cylinder 1 heater connector
Shorted channel 1 output in the heater unit

What to check, in order

Start with the simplest. You can tick off each step.

Check the connector and wiring
With the connector unplugged, check whether the signal wire is making contact with ground.
Use live data to compare the reading with actual conditions
Measure power, ground, and signal
Replace the sensor if the circuit is good

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P23D3 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
3: Ignition and misfires
D3: Specific fault in that system

Frequently asked questions

Can I keep driving with code P23D3?

You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.

What causes code P23D3?

The most common causes are: cylinder 1 heater wire chafed to ground on the intake or engine; heater at cylinder 1 shorted to its housing; fuel or water in the cylinder 1 heater connector.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.