Jaguar XJ40 Won't Crank, Just Clicks
On the XJ40 a click and no crank is usually the battery, its connections or the gear selector switch — the starter itself comes last. Watch the dash as you turn the key, check the inertia switch, then bridge the starter relay: those free tests tell you which half of the circuit to chase.
How bad is it · Garage, carefully
Stranded rather than unsafe
Bridging the starter relay bypasses the gear interlock, so put it in Park or Neutral with the handbrake on first. A battery clamp that gets hot is a fire risk: stop cranking and find the bad joint.
Which one applies to yours depends on your symptoms, your model year and what has already been done to it.
Likely causes, most common first
Read the check cost before the odds: a free check that rules a cause out beats a likely guess that costs money.
A flat or tired battery
The starter wants several hundred amps. A weak battery can still light the dash but can't hold voltage once the starter loads it.
Rapid clicking with the lights dimming, or nothing at all after the car has stood. Below a certain voltage these cars don't grunt — they simply refuse.
Charge it fully, then measure while someone cranks. For example, 12.5 V at rest falling to about 10 V on the starter means the battery is finished.
Charge overnight or fit a new battery; jump with heavy, truck-grade leads, not thin ones.
Battery cables, the bulkhead positive stud and the earth straps
The battery lives in the boot and its positive lead ends on a stud through the bulkhead, which corrodes on both sides. The engine sits on rubber mounts and returns current only through its braided straps.
A click with a good battery; a jump that changes nothing; it starts after you wiggle a battery cable. A negative clamp that gets hot or melts its insulation is a bad earth or a shorted starter.
Battery disconnected first — the stud is always live. Clean clamps, the bulkhead stud on the engine-bay and cabin side, and the straps from engine and bell-housing to the body, to bright metal.
Clean, tighten and grease every joint; renew a strap or cable that is corroded inside.
The gear selector switch (start inhibit)
The starter relay only gets its earth when the gearbox switch reads Park or Neutral. On the 4.0 it's a rotary switch on the side of the gearbox; on the 2.9, 3.2 and 3.6 a linear switch beside the J-gate. Its peg can snap, and adjustment drifts.
Dash fine, a relay click, no crank. The gear indicator under the gauges goes blank, sometimes with cruise control dead or the BRAKE warning lit in START. It can follow a forced shift across the gate: a snap from under the J-gate, then the gear lamps on the J-gate go dark too.
Try Neutral with your foot on the brake, then move the lever a fraction off Park. If the indicator comes back and it cranks, it's the switch or its adjustment. If bridging the starter relay under the dash makes it crank while the key won't, the start signal is blocked upstream and this switch is the first suspect. With the selector out, look for damage and try sliding it on its slotted bolt holes.
Re-align the switch until Park shows and both cranking and reversing lights work; replace it if the peg has broken. The linear switch is DBC12395; the wood trim around the selector has to come off to reach it.
The ignition switch, or its earth
The electrical switch behind the steering lock feeds positions II and III. Its contacts wear, and a poor earth to it kills START the same way.
Silent in START with the gauges and headlights dead, while the radio and fans still work; or a relay click that only turns into cranking after several tries.
If bridging the starter relay cranks the engine but the key doesn't, look at the switch and its earth. The switch can be checked with an ohmmeter position by position.
Contact cleaner into the switch, worked through its positions many times, as a stopgap; a new switch or a repaired earth for good.
The starter motor and solenoid
Solenoid contacts burn, especially after starts on low voltage; brushes wear and the pinion can hang up. I'd rule out the connections and the relay before the starter.
A click from the starter itself but no turn, odd noises for a few days first, graunching or smoke from the starter. A few sharp taps on the case get it going once more.
Relay bridged and good voltage on the thin white wire at the solenoid, yet no crank — it's the starter. That wire passes a big round connector on top of the engine, so measure there too.
A rebuilt starter with a new solenoid. Take the wiper assembly off to reach the top bolt, a 13 mm head on an M10 x 85 bolt (FB110171); the lower one from underneath.
The inertia switch has tripped
The impact switch cuts everything fed from key positions II and III. Hazards, blower, radio, locks and windows keep working, so the car looks half alive.
No crank with the gauges, headlights and wipers dead, often after work in the footwell.
Find the small switch low in the footwell near the pedals: a popped-up button with a red band means it has tripped.
Press the button back down.
The starter relay and its relay board
On earlier cars the start relay sits in the panel behind the passenger knee bolster. From 1993 it's position 4 of 4 in relay module G, a blue-based box under the glovebox, and the coil joints on that board crack.
One click and no crank; or it refuses after a warm stop and comes back later. Pressing the relay closed by hand starts the car.
Selector in Park or Neutral, handbrake on. Pull the relay and bridge pins 30 and 87, brown to white: if it cranks, the starter is fine and the fault is on the relay side.
Worth trying: clean the relay contacts or reflow the cracked joints on the board; a used module needs the same treatment.
An alarm or security start inhibit
An alarm with its own start inhibit can stay latched after the battery has gone flat. The factory security switch in the centre console box also disables starting.
No crank after a flat battery or a battery change, with everything else normal.
With a charged battery, lock and unlock with the fob a few times; check the console security switch.
Worth trying: arm and disarm the alarm, or reset the security switch.
The central processor: cold, water or a cracked joint
On 1993-on cars the starter relay is switched through the body processor. Water from a leaking windscreen seal or a cracked solder joint stops it, often only in the cold.
No crank together with dead locks, interior lights and wipers, typically on a freezing morning, back to normal as it warms; wet front footwells.
Look for water in the footwells; remove the processor, check it for damp and corrosion, and reseat its connector.
Worth trying: wash and dry the processor, or fit a used one.
The order to check them in
The point of the order is money: each step either rules a cause out or makes the next one worth doing. Green is free, amber costs a little, red is the one to arrive at last.
Selector in Park, then Neutral, foot on the brake
If it cranks off Park or the gear indicator comes back, it's the selector switch.
freeWatch the dash as you turn the key
Gauges and headlights dead: inertia switch or ignition switch. Lights dim to nothing or rapid clicking: battery or connections. One click and no dimming: relay, inhibit or starter.
freeCheck the inertia switch button
A red band showing means it has tripped; press it down.
freeCharge the battery and measure while cranking
Around 10 V or less on the starter means the battery or its joints can't deliver.
freeClean the clamps, the bulkhead stud and the earth straps
Battery disconnected first. Do both sides of the bulkhead stud.
freeBridge the starter relay, pins 30 to 87
Park or Neutral, handbrake on. Cranks: relay, inhibit or ignition switch. Doesn't: the starter or its feed.
freeClean or resolder the relay
On 1993-on cars it lives in relay module G under the glovebox.
free, or a relayOnly then the starter
Tap it first; if it still won't turn with full voltage at the solenoid, rebuild or exchange it.
a rebuild, about $140What it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar XJ40 Cranks But Won't StartIf it turns over normally but won't fire, start there.
- Jaguar XJ40 Battery Drain, Flat After a Few DaysIf it clicks because the battery goes flat after standing a few days.
- Jaguar XJ40 Alternator Not Charging, Battery LightIf the battery never seems to stay charged.
- XJ6 (XJ40) fuse boxes and relaysOther years from the same page.
- Jaguar XJ40 Immobiliser Problems, Won't StartIf the alarm sounds, the remote does nothing or it started after a flat battery — the security system.
- Jaguar VIN decoderConfirm your exact model year, engine and factory options before ordering parts — free.
Ratings, fuse numbers and torque figures vary by model year and market. Read the legend on your own car before pulling anything, and use the figures in the manual for your car, not the ones in a video.
Check your VIN: exactly which car you have and which bulletins apply to it.