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Install a Car Battery

How to install a car battery

Disconnecting the car battery causes a loss of critical settings

You can’t just yank the battery cables off a car battery on a late model vehicle to install a car battery without causing some problems. Most late-model vehicles include many electronic devices that require power to maintain their memory. When you disconnect the battery terminals here’s what happens:

• The PCM loses its Keep Alive adaptive memory. On start-up the PCM will revert to factory settings and that may cause the engine to run poorly because the air/fuel mixture is too rich or too lean. With the loss of Keep Alive Memory, you may also notice a difference in the way the transmission shifts, with harsh shifts or shifts that occur at different times. That will continue for about the next 10 cold start ups while the PCM relearns the optimal settings.

• Loss of throttle body calibration that can cause a no-start or loss of acceleration with the new battery. Many car brands require a throttle body relearn procedure (Nissan and VAG VW vehicles). While other brands will relearn throttle body calibration simply by starting the engine and letting it idle for a set period of time.

• On some Ford vehicles, loss of battery power resets the FMEM (Failure Mode Effects Management) module. The module then substitutes estimated or fixed data for missing sensor data.

• The ABS (Antilock Brake System) and SIR (Supplemental Inflation Restraint) modules reset. On some vehicles, the modules requires a special relearn or reprogramming procedure after power has been lost. Until the relearn is performed, that may prevent the ABS or airbag systems from working.

• The Climate Control module may reset, requiring a relearn procedure to recalibrate the blend and mode door actuators. On some vehicles, the loss of battery power causes the climate control to stop working completely until a relearn is performed with a factory scan tool.

• The Body Control Module (BCM) resets and may require a relearn or reprogram. This can result in the loss of power accessories like power windows, memory seats, power sunroof, or electronic suspension settings.

• Possible no start due to reset of anti-theft systems. so the engine may crank but not start, or start and then stop.

• Loss of power window and/or power sunroof position calibration. For power windows, that can mean the loss of the auto-up feature. For sunroofs, the loss may require a calibration to relearn the full open and full closed positions.

• Loss of steering angle sensor settings. The steering angle sensor may have to undergo a relearn procedure following battery disconnect or replacement.

• And, of course, loss of power causes a loss ob all radio and clock settings. This is more of an annoyance than a problem, and can be fixed by resetting the radio channels and the time.

image of accelerator postion sensor and electronic throttle body

The gas pedal sends electronic signals to the PCM which then tells the throttle body how far to open

Connect a backup power supply when changing a car battery

The best way to avoid having to tow your car in for reprogramming is to avoid losing the memory in the first place. Here’s how to do that.

Follow this procedure to prevent damage to vehicle electronics

WARNING: Vehicle computers often stay “awake” for up to 45 minutes after removing the key form the ignition. If you attempt a battery replacement using backup power through the OBDII port, the power draw from those modules can cause damage to the OBDII port terminals or the ESA 30 cable. It may also cause ECM or other module fuses to blow.

Connect the ESA30 cable to the OBDII port and route it through an open window. Wait 45 minutes after key removal before connecting the cable to a jumper pack or power suppply.

If you have an amp probe, you can connect it to the negative battery terminal and monitor current draw to determine when the modules have gone into sleep mode.

You’ll need a jumper pack or an AC-DC power converter, and you’ll need a special OBDII cable. The SOLAR #ESA30 cable is about $16. You can pick up a battery-powered jumper pack at any auto parts store or Walmart for under $50. car jumper pack

DO NOT OPEN ANY DOORS OR TURN ON THE KEY DURING THIS PROCEDURE. THAT CAN WAKE UP THE MODULES, CAUSING  EXCESSIVE POWER FLOW THROUGH THE OBDII PORT.

1) Remove the key from the ignition.

2) Plug the cable into the OBDII port. Run the cable through an open window and close the door. Wait 45 minutes for all modules to go into “sleep” mode.

3) Then plug the cigarette lighter end into the jumper pack.

4) Disconnect the negative battery cable. Then remove the positive cable and INSULATE it—it’s live. I usually throw it inside a leather glove.

5) THEN you can remove the dead car battery.

6) Lift the old car battery out, making sure you don’t dislodge the insulator on the positive terminal.

6) Clean the battery tray and all the hold-down connections. If the threads on the J-bolts are corroded, clean them with a wire brush and apply a light coating of anti-seize. If the hold-down clamps or brackets are rusted, spray them with a battery acid neutralizer products. Then dry and spray with a fresh coat of paint.

7) Clean the posts on the new car battery and the cable terminals using a wire brush. Then install the car battery onto the battery tray.

8) Position the top bracket. Then install the positive battery cable first and then the negative cable. Make it a quick push-on affair—you want to avoid arcing that can damage computers. Tighten the hold-down bolts and nuts. Once the new battery is installed, you can disconnect the ESA30 cable from the jumper pack.

This procedure keeps the PCM fully powered up and prevents it from losing all it “adaptive memory.” So you can start the engine and go without the PCM having to relearn all the values.

change car battery, install car battery

Keep memory alive with a jumper pack and OBDII adapter cable.

NOTE: Ricksfreeautorepairadvice.com receives a commission on items purchased using this amazon link.

Need to charge your car battery? Click here for instructions

If your battery terminals are corroded, replace them. Click here to see how.

© 2012 Rick Muscoplat

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