Technical Analysis of Code P1336: Random Misfires in 1.6 and 2.0 PSA Engines

Introduction to P1336: The Nightmare of Random Failures

If you work with the PSA (Citroën/Peugeot) line, you know that the code[glossary]DTC[/glossary]P1336 is one of the most challenging diagnoses in 1.6 16v (TU5JP4/EC5) and 2.0 16v (EW10A) engines. Unlike codes that point to a specific cylinder (such as P0301 to P0304), P1336 indicates “Random or indeterminate misfire with risk of catalytic converter destruction”. In practice, the vehicle exhibits excessive vibration, severe power loss (the famous “emergency mode”), and the warning light.[glossary]electronic injection[/glossary]The light flashes and, in many cases, the system deactivates the injector nozzle of the missing cylinder to protect the engine, which confuses the novice mechanic who thinks it is a permanent component failure.

Probable Causes and Analysis of Correlated DTCs

Error P1336 rarely occurs alone. It is the main symptom of an irregularity in the crankshaft rotational speed detected by…[glossary]ECU[/glossary](Engine Control Unit) via the rotation sensor. The causes range from basic maintenance items to complex software or internal mechanical failures.

• Ignition: Coils with current leakage or spark plugs with resistance outside the OEM standard.
• Food: Low fuel line pressure or uneven fuel injector flow.
• Mechanics: Carbon buildup on the intake valves or loss of compression.
• Electrical: Problems with the wiring harness or[glossary]BSM[/glossary](Engine Service Box).
• Synchronization: [glossary]Timing belt[/glossary]loosened or out of point by one tooth.

You will often find associated codes such as P0300 (Multiple Misfire), P1337, P1338, P1339, or P1340, which indicate in which cylinder the misfire started before becoming random.

Location of Fuses and Electrical Components

Before disassembling the engine, check the power supply to the ignition and injection system. In the Citroën C4 or C3, the engine fuse box (BSM) is the critical point.

Check for signs of oxidation on the BSM pins, which causes voltage drop and generates the P1336 error intermittently.

Step-by-Step Diagnosis

1. Real-Time Data Analysis

Use a[glossary]scanner[/glossary]Use an automotive diagnostic tool (preferably Diagbox or Lexia) to monitor the “Misfire Count” parameters. Note if the misfires increase under load (rapid acceleration) or at idle. If the misfires only occur with a cold engine, the main target is carbonized valves or a faulty temperature sensor.

2. Ignition System Test

Remove the ignition coil (usually a ruler type in 1.6 and 2.0 engines). Check for cracks in the plastic body. Use an oscilloscope to analyze the firing time and firing voltage. Spark plugs should be checked with a gauge: the gap must be exactly 0.9mm for Flex engines.

3. Pressure and Flow Rate Verification

Connect a pressure gauge to the fuel line. The pressure should remain stable at 3.5 bar (1.6 engines) or 4.2 bar (2.0 engines with a returnless system). If the pressure drops rapidly after turning off the engine, a nozzle may be leaking, causing error code P1336 on startup.

4. Checking the Crankshaft Position Sensor (CKP)

The P1336 is generated by microsecond variations in the reading of[glossary]rotation sensor[/glossary]If the sensor is dirty (iron filings) or the wiring harness is dry and brittle, the ECU will lose accuracy in calculating combustion.

Technical Solutions and Procedures

After identifying the culprit, follow the assembly guidelines:

1. Spark Plug and Coil Replacement: Always replace the entire assembly. Aftermarket coils often lack the necessary electromagnetic shielding, generating noise that confuses the ECU and keeps the P1336 error code active.
2. Chemical Cleaning (Decarbonization): In high-mileage engines, carbon buildup on the valve heads absorbs fuel during the cold start phase. Use specific products (via intake) or disassemble the cylinder head if the compression is below 150 PSI.
3. Teleloading (Update): In many cases of C3 and C4 models with the 1.6 Flex engine, error code P1336 is a flaw in the original software strategy. The solution is to reload the ECU with the corrected software via the PSA server.
4. Rotation Sensor Learning: After any intervention on the ignition system or timing belt, it is MANDATORY to perform the phonic wheel form learning procedure via scanner. The engine must be warmed up to 80°C and accelerated to the rev limiter (approx. 5000 RPM) in free deceleration.

Parts, OEM Codes and Torques

Always work with top-quality parts to avoid returns.

• Spark Plugs: NGK LFR6B (OEM) or Iridium LFR6AIX.[glossary]torque[/glossary]Tightening force: 25Nm to 30Nm.
• Ignition coil: Valeo 245041 or Delphi GN10232. OEM code: 597087 (1.6 engine) / 597099 (2.0 engine).
• Rotation Sensor: Bosch or NTK. OEM code: 1920GV.

Costs and When to Use the Dealership

In the Brazilian market, the repair cost for a P1336 error varies drastically:

• Basic maintenance (spark plugs + injector cleaning): R$ 400.00 to R$ 700.00.
• Premium coil replacement + spark plugs: R$ 800.00 to R$ 1,200.00.
• Wiring harness or BSM repair: R$ 600.00 to R$ 1,500.00.

The owner should contact the dealership specifically when the diagnosis indicates the need for **Tele-uploading (software update)**, as only workshops with access to the PSA Token system can perform this security update, which is often the only definitive cure for P1336 in older Flex models.

Prevention

To prevent the P1336 error from recurring, recommend that the customer use fuel of known origin (avoiding excess solvent which attacks the injector seals) and replace the spark plugs every 30,000 km, even if the manual suggests longer intervals. In PSA engines, a worn spark plug increases the load on the coil, which in turn fries the ignition coil.[glossary]transistor[/glossary]The ECU output will either cause a random combustion error or generate a random combustion error.

Diagnosing the P1336 fault code is a test of patience and precision. Don’t start replacing parts by trial and error. Use an oscilloscope, check the mechanical components, and above all, ensure the electrical system is intact.