Whenever a vehicle is jump started, precautions must be followed in order to prevent the possibility of personal injury. Remember that batteries contain a small amount of explosive hydrogen gas, which is a by-product of battery charging. Sparks should always be avoided when working around batteries, especially when attaching jumper cables. To minimize the possibility of accidental sparks, follow the procedure carefully.
Trucks equipped with a diesel engine may utilize two 12-volt batteries. If so, the batteries are connected in a parallel circuit (positive terminal to positive terminal, negative terminal to negative terminal). Hooking the batteries up in parallel circuit increases battery-cranking power (amperage) without increasing total battery voltage output. Output remains at 12 volts. On the other hand, hooking two 12-volt batteries up in a series circuit (positive terminal to negative terminal, positive terminal to negative terminal) increases total battery output to 24 volts (12 volts plus 12 volts).
Jump Starting A Dual Battery Diesel
Diesel model vehicles utilize two 12-volt batteries, one on either side of the engine compartment. The batteries are connected in a parallel circuit (positive terminal to positive terminal and negative terminal to negative terminal). Hooking the batteries up in a parallel circuit increases battery-cranking power without increasing total battery voltage output. The output will remain at 12 volts. On the other hand, hooking two 12-volt batteries in a series circuit (positive terminal to negative terminal and negative terminal to positive terminal) increases the total battery output to 24 volts (12 volts plus 12 volts).
In the event that a dual battery vehicle needs to be jump-started, use the following procedure:
- Turn the heater blower motor ON to help protect the electrical system from voltage surges when the jumper cables are connected and disconnected.
- Turn all lights and other switches OFF .
- Connect the end of a jumper cable to one of the disabled diesel's positive (+) battery terminals, then connect the clamp at the other end of the same cable to the positive terminal (+) on the jumper battery.
- Connect one end of the other jumper cable to the negative battery terminal (-) on the jumper battery, then connect the other cable clamp to an engine bolt head, alternator bracket or other solid, metallic point on the disabled vehicle's engine. DO NOT connect this clamp to the negative terminal (-) of the disabled vehicle's battery.
- Start the engine on the vehicle with the good battery and run it at a moderate speed.
- Start the engine of the vehicle with the discharged battery.
- When the engine starts on the vehicle with the discharged battery, remove the cable from the engine block before disconnecting the cable from the positive terminal.
Jump Starting Precautions
Single Battery Vehicles
- Make sure that the voltages of the two batteries are the same. Most batteries and charging systems are of the 12-volt variety.
- Pull the jumping vehicle (with the good battery) into a position so the jumper cables can reach the dead battery and that vehicle's engine. Make sure that the vehicles Do NOT touch.
- Place the transmissions of both vehicles in NEUTRAL or PARK , as applicable, then firmly set their parking brakes.
- Turn off all lights and accessories on both vehicles. Make sure the ignition switches on both vehicles are turned to the OFF position.
- Cover the battery cell caps with a rag, but do NOT cover the terminals.
- Make sure the terminals on both batteries are clean and free of corrosion or proper electrical connection will be impeded. If necessary, clean the battery terminals before proceeding.
- Identify the positive (+) and negative (-) terminals on touching should one loosen during the procedure. Do NOT connect this clamp to the negative (-) terminal of the bad battery.
- Check to make sure that the cables are routed away from any moving parts. Start the donor vehicle's engine. Run the engine at moderate speed for several minutes to allow the dead battery a chance to receive some initial charge.
- With the donor vehicle's engine still running slightly above idle, try to start the vehicle with the dead battery. Crank the engine for no more than 10 seconds at a time and let the starter cool for at least 20 seconds between tries. If the vehicle does not start in three tries, it is both battery posts.
- Connect the first jumper cable to the positive (+) terminal of the dead battery, then connect the other end of that cable to the positive (+) terminal of the booster (good) battery.
- Connect one end of the other jumper cable to the negative terminal on the booster battery and the other cable clamp to an engine bolt head, alternator bracket or other solid, metallic point on the engine with the dead battery. Try to pick a ground on the engine that is positioned away from the battery in order to minimize the possibility of the two clamps likely that something else is also wrong or that the battery needs additional time to charge.
- Once the vehicle is started, allow it to run at idle for a few seconds to make sure that it is operating properly operating.
- Turn on the headlights, the heater blower, and (if equipped) the rear defroster of both vehicles. This will reduce the severity of voltage spikes and subsequent risk of damage to both vehicles' electrical systems when the cables are disconnected. This step is especially important to late model vehicles equipped with computer control modules.
- Carefully disconnect the cables in the reverse order of connection. Start with the negative cable that is attached to the engine ground, then the negative cable on the donor battery. Disconnect the positive cable from the donor battery and finally, disconnect the positive cable from the formerly dead battery. Be careful when disconnecting the cables from the positive terminals to NOT allow the alligator clips to touch any metal on either vehicle or a short and sparks will occur.