The first generation of Prince (THP) engines features variable cam timing on the intake cam. This means that it can be advanced or retarded based on what is requested by the ECU calibration software. Newer engines like THP200 feature variable cam timing on both cams.

THP (Prince) engine cam shaft and variable cam timing mechanism

THP (Prince) engine cam shaft and variable cam timing mechanism – you can see the cam phaser to the right of the camshaft

How it works

Oil pressure from the oil pump goes into a solenoid valve on the engine block. This valve controls the oil pressure that reaches the cam phaser. The cam phaser is the adjusting mechanism which controls intake cam timing. The cam timing changes depending on the oil pressure inside the cam phaser.
The whole system after the cam oil pressure solenoid valve is purely mechanical. There are no pressure sensors providing feedback about what goes on into the cam timing mechanism with regards to oil. Which means it can cause undetectable trouble when something malfunctions.
If you want to read more on the system, from the people who design and produce it, you can check Delphi:


Problem 0 – Stuck or malfunctioning oil control solenoid

The solenoid valve gets contaminated with dirt that accumulates from the oil residues over time. This leads into the system getting stuck and feeding less or more pressure into the camshaft. This valve sits next to the hydraulic chain tensioner – intake side.

Cam solenoid valve

This is the solenoid valve that adjusts oil pressure to the intake cam shaft variable timing mechanism

Cam solenoid valve

cam timing solenoid, contaminated with engine oil residues

Problem 1 – Oil leaks from oil rings and the camshaft’s end

The camshaft has oil rings at its end to make sure that the oil goes through it and on to the cam phaser. If the oil rings get damaged, the oil leaks. Pressure drops before reaching the cam phaser. This is what happened in the following photo.

THP (Prince) engine cam shaft end with worn oil rings

THP (Prince) engine cam shaft end with worn THP (Prince) engine cam shaft end with worn oil rings. These ones had been leaking oil, causing all sorts of problems

THP (Prince) engine cam shaft, noting position of the oil rings

THP (Prince) engine cam shaft, noting position of the oil rings


Problem 2 – Stuck cam phaser mechanism

The adjusting mechanism itself can get stuck. Or if the spring inside it weakens, it can start misbehaving.


Potential fault codes caused by these problems

  • System too lean
  • System too rich
  • Both of the above at the same time
  • Super-knocking and misfires
  • Excessive fuel consumption together with crazy fuel trim values
  • Erratic acceleration and torque loss

How to fix them

It is always a good idea to check engine oil pressure, before touching any of the above components. If there is insufficient oil pressure it can be the root cause of all these problems, without any parts being at fault.
Otherwise, the only way to fix these problems is to inspect each individual part first and then start replacing them:

  1. The cam oil control solenoid
  2. The cam shaft oil rings
  3. The cam phaser


Many thanks to Khaled for figuring out this crazy problem!


  • Jonathan Martinez Alegria Posted October 31, 2016 9:48 pm

    Hello from Mexico.
    It will be nice if you can post the part numbers of the solenoid part and oil rings.

    • Jonathan Martinez Alegria Posted June 29, 2019 5:41 am

      Answering to myself, oil control solenoid part is: 1922R7

  • Charles Posted October 1, 2017 6:15 pm

    Thanks for this ! it’s very interesting !

  • Arthur Porter Posted December 9, 2018 1:06 pm

    Thank you for sharing this vital information, I am beginning to realize that the compact “Prince” engine requires more than double the amount of care and maintenance especially oil changes than what is specified from the stupid manufacturer as all most of the engines problems stem from inadequate lubrication maintenance otherwise a fantastic little car!

    • Stelios Alexandrakis Posted January 27, 2019 12:27 am

      It only requires a few things to be kept in good shape. Make sure that the timing is good and the sparkplugs fresh and this engine will last you a lifetime.

  • Ilie Iulian Posted March 7, 2019 10:00 pm

    Ma confrunt cu o problema la acest tip de motor.
    L-am demontat pentru că am crezut că voi remedia problema. Misfire cilindru 3.
    Bobina schimbată, bujii, senzor temperatură lichid răcire.
    Motorul merge bine până la temperatura de 80 Gr. apoi merge in 3 și pornește ventilatorul de răcire.
    Am găsit uzură pe lagărele de la axele cu came și pe cilindri. Am înlocuit axe și supape , merge la fel….
    Aștept sfaturi de la cei care pot da!

    • dan Posted May 24, 2019 12:50 pm

      Ai rezolvat problema?

      Incepe si la mine aceeasi poveste.
      Am un 308 T9 sau MK2 din 2014 cu THP 1.6 (156cp).
      La un drum pe viscol asta iarna dupa ce am stat vreo 2 ore oprit intr-o coloana (la ralanti) am primit o eroare
      “Engine Fault Repair Needed” si s-a oprit motor/lumini, tot.
      Dupa vreo 2 chei a luat-o dar nu mai avea putere am mers cu a 2 vreo 10 Km (inca eram in coloana dar
      oricum ma chinuiam sa ma tin dupa un tir).
      Dupa astia 10 – 11 km si-a revenit brusc.
      Dupa asta nimic pana in Mai cand la dupa un drum scurt 10 km mi se aprinde becul de ulei.
      Ma duc la service si le zic sa se uite si la codurile de eroare.
      Ei imi zic ca bobina de la cilindrul 3 trebuie schimbata sau lantul de distributie.
      Am schimbat intai bobina. Dupa schimbarea la ralanti (stop, dupa pornire) masina tremura sesizabil.

      Multumesc pentru raspuns (daca).

  • Simon Posted March 23, 2019 1:47 am

    Is there an easy way to tell if the cam oil seals are worn?

    • Stelios Alexandrakis Posted April 6, 2019 10:16 pm

      Unfortunately not unless you remove and inspect the camshafts.

  • Christian Posted June 13, 2019 12:02 am

    Did PSA make any major improvements for the second generation of the thp 155 engine? (Stronger Timing chains, etc)

  • FRANCO Posted July 19, 2019 9:05 pm


    • Costi Posted September 11, 2019 10:22 pm

      Any soluționa to oil presu
      Sure to High?

  • James moore Posted August 9, 2019 7:25 am

    What’s the easy way to replace the oil rings m. I have changed them but had to use a hook tool to stretch them over the Cam. Think it’s made it worse than better

    • Petr Posted October 27, 2019 5:53 pm

      They do stretch a little biT. Not having a special tool, I used a plastic drinking straw (cut in halF) to slide them in over the cam edges to prevent damage. I guess that a hook/spoon (without sharp edges) is oK unless yoU Saw them break…

      I replaced them just bEcause the cams were down when doing the valve stem seals, so cant tell the effect on An EP6CDT/5FV. The old ones looked a-ok after almost 200k kms

  • Gary Posted February 17, 2020 7:04 pm

    Can failure of any part of this system cause low compression across all cylinders?

    as my 1,6 thp has 50psi on all cylinders and wont start , once parts are replaced does the timing have to be reset?

  • Dean Posted February 27, 2020 6:02 pm

    Hi I replaced my Camshaft dephaser pulley on my 2012 Renault Clio III 1.6 16V and kept on getting a fault code for the solenoid valve. I replaced the solenoid today but the idling very erratic and the motor wants to cut out and if I press on the gas it makes a knocking noise. Any suggestion? Thanks

  • Sam B Posted June 10, 2021 9:23 pm

    Oil ring part number is – 0807 39 (sealing ring)

  • Martin Posted November 7, 2021 3:02 am

    Hey great article,
    but got one question.
    Could you please take a photo or describe where exactly this solenoid is located?

    • Stelios Alexandrakis Posted January 9, 2022 11:03 pm

      The cam control solenoid is located at the back of the engine block, timing chain side. It looks like a very big hex nut.

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