FAQ
TL;DR: DIY C4 AL4→manual swaps reported at ~PLN 800; “The car works as if there was never an automatic machine there.” [Elektroda, intels, post #17273210]
Why it matters: This FAQ helps Citroën C4/C5 owners plan a reliable AL4-to-BE/ML gearbox conversion with minimal electrical headaches.
Quick Facts
- DIY cost reported: Approx. PLN 800 when doing all labor yourself. [Elektroda, intels, post #17273210]
- Coding: Set BSI and engine ECU from automatic to manual in Lexia; cluster updates accordingly. [Elektroda, intels, post #17186356]
- Reverse lamps: Wire the manual switch into BSM as per diagram; confirmed working. [Elektroda, intels, post #17214229]
- Gearbox codes seen: 20DM12, 20DP10 considered; 20CQ16 used successfully with TU5JP4. [Elektroda, intels, post #17186356]
- Loom handling: Keep and hide the AL4 wiring rather than cutting it. [Elektroda, Tomasz Downacki, post #16699339]
Which BE4 gearbox codes fit the Citroën C4 1.6 16V TU5JP4?
Owners researched 20DM12 and 20DP10, and one completed a swap using a 20CQ16 with shafts and clutch. Fitment depends on mounts and drives. Verify donor parts match your TU5JP4. [Elektroda, intels, post #17186356]
What coding changes are required after an AL4 to manual swap?
Reconfigure both the BSI and the engine ECU to recognize a manual gearbox. As one expert put it, “you need to reprogram the BSI and the engine controller.” Without this, the engine may not crank. [Elektroda, Tomasz Downacki, post #16695800]
Can I do the coding with Lexia/DiagBox?
Yes. Lexia handles the necessary configuration. One installer advised doing the coding and leaving the old loom hidden rather than cutting anything. [Elektroda, Tomasz Downacki, post #16699339]
Should I cut out the AL4 transmission wiring?
No. Keep the original installation and hide it. Cutting introduces risk without benefit during coding or diagnostics. [Elektroda, Tomasz Downacki, post #16699339]
How do I wire the reverse lights after the manual swap?
Connect the manual reverse switch to the BSM pins per the shared diagrams. The solution was tested and the lamps worked correctly. [Elektroda, intels, post #17214229]
How much does the swap cost if I do it myself?
One C4 owner reported spending about PLN 800 by sourcing parts and doing the labor personally. Selling the working AL4 helped offset costs. [Elektroda, intels, post #17273210]
Will the instrument cluster switch from automatic to manual display?
Yes. After coding BSI and ECU to manual in Lexia, the cluster switched from automatic to manual display mode. [Elektroda, intels, post #17186356]
Does the original starter fit after converting to manual?
Yes. The starter matched the engine casing. No starter changes were needed in the reported C4 TU5JP4 swap. [Elektroda, intels, post #17273210]
The car won’t crank after the swap—what’s the common cause?
If the system still expects an automatic, it looks for the P position and blocks starting. Recode BSI and ECU for manual to restore cranking. [Elektroda, Tomasz Downacki, post #16695800]
Can I install a 6‑speed manual instead of a 5‑speed?
Yes. A C5 3.0 V6 owner reported a working 6‑speed setup with smooth acceleration and proper operation after configuration. [Elektroda, karmazynio, post #17487379]
Do cruise control and parking sensors still work after the manual conversion?
Yes. After completing wiring and coding, cruise control and reverse sensors were reported as fully functional. [Elektroda, karmazynio, post #17487379]
I unplugged the AL4 TCU and got a BSI error—what should I check?
This can occur if modules still reference the automatic. Ensure BSI, ECU, and ESP are set to manual. Clear faults after coding. [Elektroda, karmazynio, post #17471280]
Is paying a shop worth it compared with DIY?
One member received a shop estimate around PLN 2,800, versus a DIY outlay near PLN 800. Budget, tooling, and risk tolerance decide the path. [Elektroda, matmirek, post #17305945]
Can I just short jumpers to start the car without coding?
Avoid jumper hacks. Properly reprogram the BSI and ECU to manual. That resolves the P/N start lock and keeps systems integrated. [Elektroda, Tomasz Downacki, post #16695800]
What are the basic steps to swap AL4 to manual on a C4 1.6 TU5JP4?
- In Lexia, set BSI and engine ECU from automatic to manual.
- Install the manual gearbox (e.g., 20CQ16) with matching shafts and clutch.
- Wire the reverse switch to the BSM; confirm lamp operation.
[Elektroda, intels, post #17186356]
Any reliability notes or failure edge cases to expect?
One owner reported repeated automatic failures; others note no-start until coding is complete. Plan coding first to avoid immobilized vehicles. [Elektroda, Tomasz Downacki, post #16695800]
