21 November 2022
Alternator replacement is a straightforward DIY job, even on the TDV6 engine, as Dave Barker shows
Need to know
Time: 1 hour.
Difficulty: 1 out of 5 stars
Models: Discovery 3 and Range Rover Sport 2.7 TDV6.
Tools needed: General workshop tools, including 7, 8, 13, 14mm spanners and sockets, flexible ratchet ring spanners are also an advantage, and a 3/8-inch square drive bit, plus a thin 36mm spanner and a suitable tool to hold the electric fan pulley (Land Rover special tools 303-1142 and 303-1143).
Parts needed: Alternator (YLE500400), prices range from around £165 to £890 for a Genuine Land Rover replacement. The most popular brand, Denso, is around £225.
• Wear protective gloves or barrier cream to protect the hands and skin from fluids, oils and sharp edges of components.
• Before starting work, disconnect the battery following the correct procedure as recommended by Land Rover.
Contact: Maddison 4x4, Water House Farm, Station Road, Topcliffe near Thirsk, YO7 3SG. Tel: 01845 587407. maddison4x4.com
The alternator produces the current required by the vehicle’s electrical systems and it charges the vehicle’s battery. It comprises a winding around an iron core supported by bearings, plus other parts including a rectifier that converts the alternating current (AC) produced to direct current
(DC) required by the vehicle’s electrical system. A regulator controls the DC output of the alternator.
This 2008 Discovery 3 had done over 127,000 miles and was still fitted with its original alternator. It was now displaying an ignition warning light, indicating that the battery was no longer being charged. This was confirmed by further testing in the workshop using a basic multimeter set to DC volts and a scale of above 15 volts. The meter’s leads were connected, red to the positive terminal on the battery and black to the negative terminal. A charged battery should read around 12.6 volts, ours was under 12 volts. The engine was started and now, with the output from the alternator charging the battery, it should read around 14.2 to 14.7 volts. Higher or lower than this would suggest the alternator was faulty. In this case, the reading from the battery remained unchanged, indicating the alternator was not charging, and a new unit was needed. Both new and reconditioned alternators are available. The original unit fitted to this Discovery 3 was a Denso, which is the most popular and recommended replacement unit, and it is also competitively priced.
The alternator, which is a 85/150 amp unit, is located on the right-hand side (looking forward) of the engine. It’s secured in position by a single bolt at the front of the unit and two at the side. There is a single multiplug connection at the rear, along with a single heavy-duty lead from the battery on the top, located by a lug on the cable eye and secured by a nut. Replacing the alternator is simple job and it can be done with the vehicle on the ground, working from above. The most difficult part is removing the electric fan which requires a thin 36mm open-ended spanner and a special tool to hold the fan hub. These are available from Land Rover or can easily be homemade: one to hold the cooling fan pulley and stop it from rotating as the fan’s viscous coupling is loosened. Note this has a left-hand thread, so it unscrews clockwise.
Removing the failed alternator
Location: The alternator is on the right side of the engine (looking from driver’s seat) below the engine cover and upper fan shroud, which need to be removed.
Battery disconnection first: The battery negative lead is first disconnected and secured clear of the battery, then the car is left for two minutes to allow electrical energy to dissipate.
De-duct: After removing the oil filler cap, the engine cover is lifted off and the oil filler cap then replaced. Next, this air intake duct is unclipped and removed.
Clearing space: The coolant bleed hose is unclipped from the top of the cooling fan upper shroud, and the shroud can then be pulled upward to remove it.
Unplugged: The electric cooling fan on the Discovery has a single multiplug wiring connection. The clip on the plug is depressed, allowing it to be disconnected.
Special tools: While securing the cooling fan pulley with a homemade tool ,the viscous fan coupling nut (arrowed) is unscrewed – clockwise, as it has a left-hand thread.
Fan is free: Once loosened, the viscous fan is then fully unscrewed off the threaded pulley stub, and removed from the vehicle.
Access gained: With the viscous fan now out of the way, we can see and gain access to the bolts securing the alternator to its mountings.
Releasing the tension: A 3/8-inch square drive bar inserted into the auxiliary drive-belt tensioner and rotated anti-clockwise, releases the tension. The belt can now be removed from the pulley.
Tensioner off: The single bolt securing the auxiliary drive-belt tensioner to the front of the engine is removed, and the tensioner can then be lifted off.
One of three: The alternator is secured into position on its mounting at the front by a single bolt – this is the easiest of the three securing bolts to remove.
Two and three: There are two side bolts. The forward bolt is easily removed, but the rear bolt is fiddly to reach and needs a hinged ratchet ring spanner.
Move it forward: The alternator can now be manoeuvred slightly forward to lift the rubber boot off the terminal and then remove the terminal lead securing nut.
Securing lug: The heavy duty cable connection is secured in place on the terminal bolt by a lug (arrowed), this is gently released with a small flat-blade screwdriver.
Final disconnection: The alternator is now free to be pulled forward, allowing the multiplug on the back of the alternator to be disconnected and the unit removed from the vehicle.
Installing the new alternator
Ready to generate: This replacement alternator is a new Denso DAN987. Prices vary widely, so it’s worth shopping around for a good price with quick delivery.
Fit and connect: The new alternator is held in position while connecting the multiplug, and securing the cable to the upper terminal with the nut before refitting the rubber boot.
Sequence bolting: The alternator is positioned on its mounting and the three bolts refitted (front bolt first) before tightening in sequence (front upper, side front, side rear) to 45Nm.
Re-tension: The auxiliary drive-belt tensioner is refitted and the securing bolt tightened to 45Nm. It’s then held using the 3/8-inch square drive while refitting the belt.
Fan unit: The viscous fan is tightened back onto the pulley stub, remembering the left-handed thread, and the electrical multiplug is reconnected.
Final connections: The upper shroud is refitted and the coolant bleed hose re-clipped onto it, followed by the intake duct. Finally, the battery negative lead is reconnected to complete.
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