P23DB: Cylinder 3 Fuel Heater Control Circuit Low

With P23DB the cylinder 3 heater control circuit is too low, meaning the line or the heater itself has found a path to ground. Because a single heat circuit is sized for several hundred watts, such a short trips the current limit at once; Bosch describes short detection per circuit and an integrated current relay in its Flexstart unit, which then cuts only the affected channel. Cylinder 3 starts on cold fuel while the remaining heaters keep working, so the engine shows roughness on one cylinder rather than a general cold-start problem. Water entering the connector, a damaged harness clip near the rail or an internally shorted heated injector are plausible causes. No manufacturer documents P23DB publicly; CARB requires circuit monitoring. Related: P23DA, P23D9, P23DC.

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

Symptoms

One-cylinder roughness when starting cold
Other cylinders start normally
Engine warning lamp, depending on manufacturer

Most likely causes

Water in the cylinder 3 heater connector
Harness chafed through at a damaged clip near the rail
Heated injector at cylinder 3 shorted internally

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 P23DB means

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

Frequently asked questions

Can I keep driving with code P23DB?

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

What causes code P23DB?

The most common causes are: water in the cylinder 3 heater connector; harness chafed through at a damaged clip near the rail; heated injector at cylinder 3 shorted internally.

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.