Auto Q&A: Troubleshooting slow cranking

The most likely causes for slow cranking and how you might check for them.

Problems with cranking don't necessarily indicate a faulty battery.
Problems with cranking don't necessarily indicate a faulty battery. –Dreamstime/TNS

Q: My van has begun to crank hard at times as if the battery is low. So far it hasn’t required a jump start, but it’s probably only a matter of time. I had the battery tested, and it’s supposed to be OK. Can you suggest what can be checked next? I’d like to try some things before going to a shop.

Drake

A: Let’s look at the most likely causes for slow cranking and how you might check for them.

Battery condition: most batteries last about 4-7 years, depending on their environment and usage. After a lengthy drive (with a good charging system, 14 volts showing on gauge) or an overnight charge, try the following: Disable fuel or spark and crank the engine for 15 seconds with a voltmeter attached to the battery terminals, preferably the posts. If the voltage dips below 11 volts while the starter is operating, the battery is likely in poor condition. Be sure the cable connections are clean and tight. Repeat the test after cleaning/tightening if there’s any doubt.

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Discharged/low battery: Resolve this before blaming battery condition. This can be caused by insufficient charging (due to short trips mostly or poor alternator performance). Try this: With voltmeter attached to the battery terminals, turn on headlights, front and rear defroster (fan on high) and check voltage while idling. If it’s below 13.5 volts, the charging system is suspect. Check belt tension.

Parasitic drain: This is a situation where an electric component is consuming energy while parked and discharges the battery. A tiny amount is normal, to keep module memories alive. Does your slow cranking depend on how long the van has been parked (e.g., it’s worse after being parked more than overnight)? If so we’re on the right track. Try this: With the key off and doors closed, check visually for any illuminated lights _ glovebox, courtesy, rear area or under hood — and listen for anything whirring or clicking, and feel the alternator for warmth (after overnight). Testing for parasitic load using a digital volt/ammeter is the next step. Due to vehicle diversity and space limitations to explain methods, this is best referred to a pro.

Cable connections and starter condition: If it’s possible to access the starter safely and conveniently, checking voltage delivered to it while cranking will prove this one way or the other. Connect voltmeter red lead to the large starter input terminal and the black lead to bare starter metal. With a strong battery, while cranking, a reading of 11 or more volts indicates good voltage delivery (battery and cables/connections). Should the starter crank poorly with this or better voltage applied, it’s suspect. Less than 11 volts while cranking usually indicates a problem with the battery, cables or cable connections.

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Using an inexpensive digital voltmeter to check for proper vehicle readings is a safe and highly effective means of checking poor component operation when precautions are followed. Be sure to remove hand/wrist jewelry, stay clear of hot or moving components, wear eye protection, and never work beneath a vehicle that isn’t carefully supported. The meter’s high input impedance protects both the circuit and user should a boo-boo occur with connections when measuring voltage.

In most cases, voltage is checked while the circuit is active; that’s when one may see unwanted voltage drops, which are often the problem.

A good circuit will deliver 90 percent or more battery voltage (which varies with load) to the component as it’s operated. If a component works poorly with good voltage delivered to it, it’s faulty. When testing a component that doesn’t work at all, one checks for where voltage is present and where it’s not as operation is attempted.