2012 XJL 5.0 NA No start/No crank Help!
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From: Massachusetts
2012 XJL 5.0 NA No start/No crank Help!
Hello everyone!
Recently, I bought a 2012 Jaguar XJL 5.0 NA as a fun second car project (and a bargain) because the original motor suffered a blown head gasket and cracked block after the rear crossover manifold failed. Ultimately, a friend from high school who works in a salvage yard gave me a low-mileage NA 5.0 from a 2011 XF that ran well before being pulled. I verified that all of the sensors and harness part numbers matched, and swapped it into my XJ. Keeping in mind that my XJ did, in fact, run perfectly fine before the swap, it now won't crank or start. I'm at a crossroads and unsure what to do; However, I assume it's the BCM because of a completely dead battery that arose the night that I began to swap the engine; all problems seem to be BCM-related, and I never touched any ground besides the battery terminal and the main body-to-engine ground. Consulting a few experts, what's the chance at this point that it's a corrupted BCM, or, coincidentally, a bad ground or an open wire? I'll attach my handy ChatGPT recap, which includes all the major information. Thanks, everyone, and I look forward to interacting on the forum!
Regards,
Jacob
Recently, I bought a 2012 Jaguar XJL 5.0 NA as a fun second car project (and a bargain) because the original motor suffered a blown head gasket and cracked block after the rear crossover manifold failed. Ultimately, a friend from high school who works in a salvage yard gave me a low-mileage NA 5.0 from a 2011 XF that ran well before being pulled. I verified that all of the sensors and harness part numbers matched, and swapped it into my XJ. Keeping in mind that my XJ did, in fact, run perfectly fine before the swap, it now won't crank or start. I'm at a crossroads and unsure what to do; However, I assume it's the BCM because of a completely dead battery that arose the night that I began to swap the engine; all problems seem to be BCM-related, and I never touched any ground besides the battery terminal and the main body-to-engine ground. Consulting a few experts, what's the chance at this point that it's a corrupted BCM, or, coincidentally, a bad ground or an open wire? I'll attach my handy ChatGPT recap, which includes all the major information. Thanks, everyone, and I look forward to interacting on the forum!
Vehicle & Work Done
- 2012 Jaguar XJ (X351) 5.0L NA
- Engine replaced with 2011 XF 5.0L NA.
- New battery installed after the first drained (~13.3 V at rest)
- Starter motor bench-tested good (spins, solenoid works, can crank the engine when bridged).
Parts Replaced / Confirmed
- Start/Stop button → replaced, same results.
- Brake switch → replaced, confirmed in SDD ("Brake ON" when pressed).
- All fuses/relays → checked and swapped, no change.
Measured Electricals
- Start/Stop switch wiring:
- Unplugged: both signal wires ~12 V.
- Plugged in: Start Switch wires 1 and 2 sag and stay at ~6 V. When attempting to start the car, those wires drop to ~3 V.
- Grounds: visually inspected; no confirmed bad grounds yet. However, I assume it would be very coincidental, as no other components, except the main engine-to-body ground, were touched. Everything worked perfectly until the swap and the subsequent dead battery. I didn't go anywhere near the trunk or anything else; I only went to the main body and the engine strap.
Diagnostic Trouble Codes
BCM (Body Control Module):- B1249-15 – Start/Stop switch circuit.
- B108B-13 – Start/Stop switch A, open/short to ground.
- B108C-13 – Start/Stop switch B, open/short to ground.
- Also has a switch illumination DTC.
- P240A – EVAP leak detection pump circuit high.
SDD Live Data
- Start button A/B = OFF (no recognition of press).
- Brake switch = ON (works).
- Crank request = NO.
- Immobilizer status = Passed.
Other Symptoms
- Remote unlock works, but locking the fob and the lock button inside the car doesn't work.
- The trunk always opens electronically, but closing is intermittent.
Regards,
Jacob
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