Low / high cooling fans speed test on EDC15 / EDC15C7 46796045 / ?????? part numbers used on Lancia works in a confusing manner on versions with 2 FANS.
Fans run at low speed when output on B23 pin is low (open collector output from ECU). This command works properly.
Fans run at high when BOTH pins B23 and C45 are low level. But the command HIGH speed only outputs LOW level on C45. The result is N12 (right sided FAN) is the only one turning at high speed, while N11 is stopped.
I lost plenty of time debugging the FANS circuitry before I could understand the error was in the test commands execution (current ECU version 1.7 registered).
Notes:
1) If you disconnect the temperature sensor on the thermostat, fans start both at low then high speed, the ECU and relays circuitry are OK. Tested on two different LANCIA 1.9 and 2.4 JTD. When issuing ECU commands, you get the problem described upper.
2) On ALFA 156 EDC 15, relays circuitry are somewhat different / both ECU commands, low and high speed, run properly with two fans LOW and fans HIGH - this need further testing, I'll get another 156 and test again
Warning: don not fiddle with the relays commands as you may burn the ECU output; relay J29 placed between fans on LANCIA, near battery on ALFA 156, has non-standardized PIN placement codes, do not replace with "compatible" NC / NO as you'll create short-circuits.
NOTE for ALfa 156:
This bug in the test FAN commands is not applicable to Alfa 156 DIESEL 2.4 JTD 2000. This is because its power circuitry is different from LANCIA: it has 2 ballast resistors. LOW - HIGH speed is not obtained by putting fans in series, but by using ballast resistors.