Intermittent No-Crank on a 2012 Diesel Utility
A 2012 diesel ute arrives with an intermittent no-crank. The customer reports it happens about once a week, always after the vehicle has sat overnight in cold weather, and a jump start gets it going. Battery voltage at rest is 12.4 V and drops to 9.1 V while cranking. A load test at 200 A shows the battery falling to 10.2 V after 15 seconds. The starter draw is 180 A when it does crank. The customer has already replaced the battery six months ago and wants the starter replaced next. Workshop temperature is 8 °C and the vehicle has 240,000 km with visible corrosion on the engine earth strap.
1. Explain how you would decide whether the battery, the earth circuit, or the starter is the primary fault, and what measurements you would take before authorising any parts replacement.
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The reported pattern points to a cold-cranking capacity problem rather than a worn starter, because the vehicle cranks normally once started and the starter draw of 180 A is within a normal range. The 9.1 V cranking voltage is low, but that figure is measured at the battery posts and includes voltage drop across the earth path.
First, measure voltage drop from the battery negative post to the engine block while cranking. A drop above 0.2 V indicates a poor earth, and the corroded strap is the prime suspect. Second, measure drop from the battery positive post to the starter terminal; above 0.5 V suggests cable or terminal resistance. Third, repeat the load test at the manufacturer's specified cold-cranking rate rather than 200 A, and correct the result for the 8 °C ambient temperature, since capacity falls significantly below 25 °C.
Only after those tests would I decide. If earth drop is excessive, replace or clean the strap and re-test. If the battery fails a temperature-corrected test, replace the battery. The starter is last on the list because its current draw is normal.
2. The customer insists the six-month-old battery cannot be faulty. How would you explain your reasoning and document the decision so the workshop is protected if the fault recurs?
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A six-month-old battery can still fail if it has been deeply discharged, left standing at low state of charge, or was never fully charged after fitting. Age alone does not prove health.
I would show the customer the temperature-corrected test result and the voltage-drop figures, explaining that the battery's ability to deliver cold-cranking current is what matters overnight, not its age. I would explain that a jump start masks the fault by supplying external current.
For documentation, I would record the at-rest voltage, cranking voltage, load-test result, ambient temperature, voltage-drop measurements on both earth and positive paths, and the test equipment used. I would note the customer's instruction and the advice given, and have the customer sign the job sheet acknowledging the diagnosis. If the earth strap is the actual fault, I would record that repair separately so the battery decision is not confused with it. This creates a clear audit trail if the no-crank returns.