Diagnosis of Code P1351 in the Citroën Line: Pre-heating Circuit Fault

The P1351 Code Challenge in HDI Engines

If you work with Citroën vehicles equipped with diesel engines (such as the 1.6 or 2.0 HDI found in the C4, C5, Jumpy, or Berlingo), you’ve certainly come across…[glossary]DTC[/glossary] P1351. Unlike other generic codes, this is a manufacturer-specific error that points to a problem in the preheating circuit. The most common symptom is not the inability to start, as the…[glossary]electronic injection[/glossary]Modern systems are efficient enough to start the car in tropical climates like Brazil’s, even without spark plugs. The real problem lies in the regeneration of the diesel particulate filter (DPF), which requires the spark plugs to function to raise the temperature of the exhaust gases. Without resolving the P1351 error, you will soon have a clogging problem in the after-treatment system.

Probable Causes and Symptoms

The code P1351 translates as: “Pre-heating relay circuit – Relay controlled and glow plugs not supplied” (Preheating relay circuit – Controlled relay and glow plugs without power). This indicates that the[glossary]ECU[/glossary](engine control unit) sent the signal to the relay to activate, but detected that there was no current consumption or that the expected voltage did not reach the spark plugs.

• Burnt-out incandescent candles: The number one cause. Often, two or more spark plugs short-circuit or open the circuit.
• Faulty preheating relay: Failure in the component’s internal contacts.
• Oxidized wiring or connectors: Common in vehicles that travel in coastal regions or areas with oil seepage.
• High amperage fuse blown: Usually located in the Protection and Management Center (PSF1).

Location and Amperage: Electrical Part

Before disassembling the intake manifold, the diagnosis begins with…[glossary]fuse[/glossary]and in[glossary]relay[/glossary]In the Citroën Jumpy or C4, the relay is usually located near the shock absorber tower or below the battery. It is a black or gray box with a 7 or 8-pin connector and a thick positive power cable.

Step-by-Step Diagnosis

1. Relay and Power Supply Verification

Use a[glossary]multimeter[/glossary]To check if the relay input pin has a constant 12V from the battery, use an automotive scanner to perform an actuator test on the pre-heating relay. You should hear a click and measure the voltage output to the glow plugs. If the relay clicks but no power is supplied, the fault is internal to the component.

2. Glow Plug Test

This is the critical point. Do not remove the spark plugs without first testing for continuity. With the relay connector disconnected, measure the resistance between the terminal of each spark plug and ground (engine block). The resistance should be between 0.6 and 1.5 Ohms. If the reading is “infinity,” the candle is burned out. If it is 0 Ohms, it is short-circuited.

3. The danger of removal

In HDI engines, the spark plugs are long and thin. If you try to remove them with the engine cold or apply…[glossary]torque[/glossary]excessive, they they will break inside the cylinder head. ALWAYS use a high-quality penetrating oil and remove the spark plugs with the engine at operating temperature.

Solution and Procedures

If the spark plugs are identified as the problem, the replacement must strictly follow the factory specifications:

1. Clean the area around the spark plugs with compressed air to prevent debris from falling into the cylinder.
2. Remove the individual electrical connector or power strip.
3. Use an 8mm or 10mm long socket (depending on the motor model).
4. Apply a small amount of ceramic grease (anti-seize) to the threads of the new spark plug.
5. Tightening torque: Use a torque wrench. The standard value for these spark plugs is… 10 Nm to 15 Nm. Excessive tightening deforms the spark plug chamber and causes premature failure.

Parts and Reference Codes

Citroën uses components from Bosch, Beru, or NGK as original equipment. We recommend sticking with these brands to avoid ECU reading errors due to impedance variations.

• Glow Plug (1.6 HDI): Bosch 0250204002 / OEM 5960.F6
• Preheating Relay: Bitron or Nagares / OEM 9640469680
• Quality Alternative: NGK Y-504J

Approximate Costs in Brazil

Prices may vary by region, but on average:

• Candles (single unit): From R$120.00 to R$250.00.
• Control relay: R$ 350.00 to R$ 600.00 (new original).
• Labor: R$300.00 to R$800.00 (depending on the difficulty of access, especially in the C4 Grand Picasso).

Expert Tip: When should you go to the dealership?

You should seek a Citroën specialist workshop or dealership if the continuity test indicates that the spark plug is burned out, but it offers significant resistance to initial rotation. A broken spark plug in an HDI requires removal of the cylinder head or the use of extremely expensive on-site extraction tools. If you lack experience in technical extraction, do not force it. Furthermore, if the P1351 code persists after replacing the spark plugs and relay, there may be a wiring harness problem in the diagnostic return line to the ECU, something that requires the specific electrical diagram from the Citroën Service Box.

Conclusion

The P1351 error should not be ignored. Although the car may appear to be running fine, the lack of preheating will prevent DPF regeneration, leading to much more expensive problems in the future. Correct diagnosis requires more of a multimeter than a scanner, and performing the replacement requires more patience and technique than brute force.