Tesla Roadster Coolant Pump Failure

Tom Saxton
August 3, 2016

The v1.5 Tesla Roadster uses a Bosch pump to circulate fluid through the battery pack and coolant manifold. It runs continuously any time the car is either on or charging. Eventually it will fail. When that happens, the touchscreen will display error number 1426 "High current pump failure."

Amazingly, it's still possible to drive the car without the coolant pump. I drove our Roadster straight to the nearest Tesla service center to get the problem diagnosed, then straight home to wait for the repair, some 20 miles altogether. The car did complain, and reduced power, but the battery temperature bars didn't get above the happy blue zone.

While you won't get stranded immediately, you definitely want to minimize driving with a coolant pump failure; the coolant pump is an integral part of the Roadster's battery management and protection system.

Roadster owners who frequently charge at 120V may see the coolant pump fail more often simply because charging takes longer, so the coolant pump runs more. It's still a minor maintenance cost compared to the service costs associated with a gas car, especially those that have performance comparable to the Roadster.

There are at least two things that can cause the "high current pump failure" error message: the pump or the electrical connector to the pump failing.

Our First Coolant Pump Failure

Our first coolant pump failure happened on September 5, 2014, with our Roadster at 42,530 miles and just a few months past the 5-year mark. Tesla was happy to sell me a replacement pump for $373.73 plus tax, raising the total to $409.23. They wanted another $400 or so to install it. I paid an experienced former Roadster service tech about half that to do the job.

As it turns out, the pump is not Tesla-specific. It's used by a number of automakers in various vehicles. You can buy it from Amazon for under $100. The photo above shows the pump label with the part number from the pump Tesla sold me. Note the three numbers on the right hand side: 08-09-30. I believe that's the manufacture date: 2008, September 30. I purchased another one from Amazon in January, 2015, which was labeled 14-08-12; I read that as August 12, 2014.

I've got no problem with the pump failing after 5+ years. It's cheap and relatively easy to replace. The troubling thing is that the pump leaks liquid into the electrical connector. The photo at the right shows liquid dripping out of the electric connector after removing it from the pump. This causes the electric connector to corrode and eventually fail. That connector is part of a complex wiring harness. I don't even want to know what the replacement cost of that harness is, much less the labor to replace it. Fortunately, the connector itself is also available and inexpensive. So, when it fails, it can be replaced. The trick is that there are extra measures required to slow down the corrosion and keep the liquid inside the electrical cable so it doesn't leak coolant.

Second Coolant Pump Failure

I got the high current coolant pump failure message again on July 27th, 2016, with 48,989 miles on the odometer. That's less than two years and just 6,368 miles since the first failure. This time the connector was definitely dead. I went ahead and replaced both the connector and the pump since the pump is cheap and having it fail is a pain.

Here's how I replaced the Roadster's coolant pump for $115 plus a couple of hours' work.

Disclaimer This article describes the procedure that I used to replace the coolant pump and connector on a version v1.5 Tesla Roadster. Tesla service centers do it differently and use a vacuum pump to remove any air in the coolant lines. The procedure here is more of a field repair using simple tools and commonly available parts. This page is intended as a reference, not advice. If you try to do this, I take no responsibility for any adverse outcome. If you mess up the battery coolant system, it could wreck your battery, or worse.

Parts and Materials

Below are the parts I used. The links are for the parts at Amazon with prices as of July 30, 2016. When I ordered another set to replace my inventory, I shopped the other seller options and got the pump and connector for $107.21. The dielectric grease can be purchased at most auto parts places in appropriate quantity for even less than the Amazon offering.

Battery Coolant Mixture

Should you need to refill or top-off the coolant, Tesla uses a 50/50 mixture of distilled water and Sierra Propylene Glycol Antifreeze (Part #SEP003). It's available on Amazon via a third party, but at a crazy high price. It will probably be much less expensive if you can find it locally.

Step 1: Secure the Vehicle

I don't want the Roadster moving while it's up on a jack, so with the car turned off (which engages the locking pin in the gear box) and the parking brake firmly set, I go one step further and put blocks on the driver's side rear wheel.

Step 2: Raise the Passenger Side

Follow the instructions in the owners manual to jack up the passenger side of the vehicle well off the ground. The extra height helps reduce the amount of coolant that leaks out during the pump swap and aids in getting the air out of the coolant lines.

Step 3: Remove the Rear Wheel and Forward Wheel Well Liner

After removing the rear passenger side wheel, you'll find there's a panel lining the upper front portion of the wheel well. Remove the five screws (9/16" socket or nut driver) and wiggle the cover out to reveal the cavity where the pump lives.

Step 4: Locate the Pump

The photo below shows the pump in the cavity. It sits in a trough in the insulation. There are two hoses secured by hose clamps at the near end of the pump, and a 12-volt power cable that connects at the far end of the pump.

High Voltage Notice the orange cables in the background. Orange means high voltage. Stay away from them. If any of those cables seem loose or damaged, stop here and get your Roadster to a Tesla service center.

Step 5: Clean, Inspect and Test Connector

If the car is awake, wait for it to time out. Usually you can tell if the car is awake by the sound of the coolant pump running, but that doesn't work when the pump has failed. Check the trunk light. If it's on, wait until it goes off. You should also hear a quiet pan in the PEM. The car should be silent and dark before proceeding.

Position a bucket under the wheel well to catch any coolant that leaks (or gushes) out.

To free the power cable, lift the pump and carefully rotate the far end of the pump out into the wheel well (see photo at right). Remove the U-shaped retaining clip from the connector, then disconnect the cable. Let any coolant that has leaked into the cable drain out into the bucket. It should be just a few drips. Clean the connector as best you can with water and a small brush. In the photos below, the one on the left shows the connector after I cleaned it. The photo on the right shows the new and old connectors; the new one shows the retaining clip.

To test the connector, hook a voltage meter to the two pins and wake the car up (e.g. by pressing and releasing the trunk close sensor, opening or closing the charge port door, opening or closing a door, etc.). When you do this, the touch screen should beep and repeat the "high current pump failure" message. While the car is awake, you should read 5V on the pump connector. Note that it's not 12V, the car won't send 12V until the pump failure has been reset; more on that later.

If there isn't 5V on the pins, or the pins look sufficiently damaged or corroded, the connector should be replaced. In this case, I could only get a small voltage reading, less than 0.1V and the pins looked terrible, as shown below. Mostly likely, our second pump failure was really just the connector going bad.

Step 6: Replace Connector

There's a rubber boot over the back of the connector. Carefully peal it back to reveal the wires. Notice the insulation on one wire is a solid color and the other has a stripe. It should be the same on the replacement connector, and they should be in the same left-right position on the connector. On the pump body, you'll find + and - symbols next to the connector indicating polarity. When you align the wires from the Roadster harness to the wires on the new connector, use the volt meter to ensure the polarity is correct before connecting to the pump.

Cut the wires to the old connector. Leave as much wire on the harness side as possible, as you may need to do this again and don't want to run out of wire on the harness side. Once the wires are exposed, ensure they don't short together. Secure them before waking the car. If they short when powered, it may blow a fuse, or worse. Now you should be able to confirm the 5V reading and check polarity when the car is awake.

Cathy did the soldering work. She cut the wires to slightly different lengths so she could cover the individual wires with shrinktube and then cover the pair with more shrinktube, which is easier if the two soldering lumps aren't in the same spot. It's a bit of challenge to leave enough room for the shrinktube but keep things short enough that you'll be able to slide the rubber boot back over everything to make a good seal.

The photos below show the wires after soldering, and then after heating the shrinktube into place. At bottom of the photo on the right, you can see the third shrinktube that will go around both wires.

Note Don't forget to slide all three segments of shrinktube onto the wires before soldering! Also, take care to keep from letting the heat of the soldering shrink the tubes before you're ready.

Step 7: Replace the Pump

If the electrical connector needed to be replaced, it may not be necessary to replace the pump. If so, skip to the next step to reconnect the power.

To replace the pump, make sure the bucket is in position to capture the coolant, and get the new pump ready to go by removing the end caps and having it within reach. (It's good to have a helper here.) Use pliers to open and slide the hose clamps back past the lumps on the pump inlet and outlet, then remove the hoses. Try to limit the amount of coolant lost and air put into the lines. Connect the hoses to the new pump, and put the hose clamps back in place to secure the hoses.

Step 8: Reconnect Power to the Pump

Before reconnecting the power cable to the pump, make sure the connectors on the cable and the pump are clear of any debris or gunk, then apply a liberal amount of dielectric grease to both connectors; this protects the contacts from the coolant liquid and insulates them from shorting through the liquid.

Remove the retaining clip from the connector, slide the connector onto the terminals on the pump, then put the clip onto the connector. Make sure the loops of the clip go into the channels on each side, popping into the openings to lock the connector in place.

Place the pump back into the cavity, taking care not to put undue stress on the power cable.

Step 9: Refill Coolant Lines and Reservoir

If you lost any coolant fluid while swapping pumps, you'll need to refill the lines through the coolant reservoir that sits on top of the battery pack under the trunk lid. Use the 50/50 mixture of distilled water and propylene glycol antifreeze as described above.

Step 10: Use 120V Charging to Reset Error and Bleed Air From Lines

Recall that testing the electrical connector only showed 5V, but it's a 12V pump. Once the Roadster has decided the coolant pump has failed, it won't try running it until the error condition is cleared. The way to clear the error is to initiate a 120V charge.

If you disconnected the pump lines and lost any fluid, or introduced any air into the lines, leave the passenger side of the car lifted up so the tires on that side are a foot or so off the ground. This is necessary to get the air bubbles out of the coolant lines. The preferred way to bleed the lines is to use a vacuum pump, but lacking that, running a 120V charge with the passenger side elevated seems to do the trick. Let the charge run for at least an hour, or until the coolant is no longer frothy.

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