Peugeot 407 EW10A Not starting, not cranking.

[teephart]

I recently purchased a used 2008 Peugeot 407.

I noticed the engine was vibrating and discovered that one of the cylinders was not firing. After conducting some tests, I replaced the spark plug, and the engine started running normally.

However, after a few days, I noticed the engine was not running stably. I performed a diagnostic scan, but there were no misfire codes on any cylinder. Instead, I found a fault code related to the VVT solenoid short-to-earth. Upon tracing the wiring, I discovered that a cable was peeled. I lifted the cable, and the engine stabilized.

While the engine was running, I attempted to insulate the exposed wire, but the +Ve line shorted to earth (-Ve), causing the engine to shut down. One or two fuses in the PSF1 (BSM-L02) were blown, which I replaced. However, the engine failed to start—there was no crank, and the starter did not engage.

I was able to jump the starter solenoid to +Ve, which made the starter rotate, but the engine still didn’t start.

I then replaced the PSF1 (BSM-L02) with another unit, but the engine still won’t start, and there are no fault codes.

While troubleshooting, I noticed that the ECM gets hot and loses communication with the BSI. Further diagnosis revealed a short circuit on one of the sensors in connector 32V GR, which I traced to the butterfly valve (1262) and the air temperature sensor (ATS 1312). The wiring appears to be intact, so I’m unsure how the devices could be causing a short circuit in the ECU.

Assistance Needed:
Troubleshooting: I need help diagnosing why the car won’t start after the short circuit.
Wiring Schematics: The schematics I’m using seem incorrect, so I need the correct wiring diagrams for this model.
Any guidance would be greatly appreciated.

[wurlycorner]

Sounds like you've done really with the fault finding so far, there.
My first port of call from where you are right now would definitely be to solve the known identified short circuit to see if that gets the ECM back on line (though if it's getting hot I'd suspect that's been damaged and will need replacing after the short circuit is repaired).
I'm not familiar with that engine or car so can't offer any further assistance unfortunately but hopefully someone will be able to provide the relevant wiring diagrams.

[teephart]

Sounds like you've done really with the fault finding so far, there.
My first port of call from where you are right now would definitely be to solve the known identified short circuit to see if that gets the ECM back on line (though if it's getting hot I'd suspect that's been damaged and will need replacing after the short circuit is repaired).
I'm not familiar with that engine or car so can't offer any further assistance unfortunately but hopefully someone will be able to provide the relevant wiring diagrams.

Thanks for your comment.
After resolving the short circuit on the VVTI Solenoid Line, the ECM came back online. However, I had to abandon the car that day and continued troubleshooting the following morning.
The next day, when I returned, the ECM was no longer online. Upon inspection, I found that there was no power to the ECU again. The fuel pump had failed, causing another short circuit in the fuse box. I unplugged the ECU, but it still wouldn’t come online.
Considering that the ECU output line can easily short to the ground, why isn’t there a protection circuit, such as optocouplers, to prevent damage from short circuits at the output?
It’s frustrating that the ECU can fail so easily.

I would appreciate it if I could get a precise and accurate engine electrical drawing for that model EW10A. The one I am currently using, "Carmin," is inconsistent and incorrect.

[teephart]

UPDATE:
I opened up the ECU and discovered that one of the power management ICs was heating up abnormally—likely due to a short circuit that damaged the IC. I replaced the ECU with another unit (unlocked), and now communication is restored and most systems are back online.

However, the engine now cranks but won’t start.

There are no critical error codes showing—just faults for the upstream and downstream O2 sensors (unplugged) and a fan chopper relay short-circuit. These shouldn't prevent the engine from starting.

I'm still actively troubleshooting and will provide further updates as I narrow down the issue.

[wurlycorner]

Well done sticking with it - hope you get to the bottom of it and look forward to the updates!

[teephart]

Do you have any ideas or suggestions as to why the engine cranks but won't start?

There are no error codes. The crankshaft position sensor (CPS) is sending RPM values between 150–400 RPM while cranking.
From my research, I learned the MAP sensor value should be around 300–450 mBar. However, when I checked the live data, it was reading about 980 mBar at a throttle position of 5.17°. It seems like the lower value is not achievable. I removed, cleaned, and serviced the MAP sensor—I believe it's working fine now, air temp was about 31° C ( weather is hot in my Location)
I'm not sure what else to check at this point, i plan to remove the ignition coil and spark plugs next to check for spark.
Any ideas or suggestions are welcome.

[teephart]

UPDATE:
The engine finally started and is running very well.
The issue was with the battery—it was draining too quickly during cranking.
I had to use a good new battery to crank it for a longer period, and after two attempts, it came back to life.