Measuring voltage drop is the most-accurate way to check any electrical connection – including a starter ground.
A bad starter ground does not occur every day. But when it does, uninformed technicians may waste untold time identifying the problem. For example, techs may completely overlook the ground because they are obsessed with the power-supply or “hot” side of the starter circuit. Other times, techs rely solely on visual inspections or judge a ground’s integrity based on hearsay. (I will return to hearsay later in this article.)
Transmission specialists will save time and aggravation by practicing reliable, straightforward starter ground checks. These are timely tests because techs usually disturb the starter ground circuit when they R&R a transmission. This happens because they usually disconnect the negative battery cable – not to mention remove the starter – during that R&R.
RETURN PATH TO BATTERY
A typical starter ground path goes from the starter housing to the engine block. Or, it runs from the starter housing to the transmission case and then to the engine block. The negative battery cable completes the ground circuit from the block to the negative battery post.
Occasionally a starter ground path goes from the transmission or block over to the vehicle’s frame. In this setup, a cable or robust ground strap connects the engine/trans assembly to the frame. Then the path runs along the frame to the negative battery cable, which is bolted to the frame somewhere inside the engine compartment.
Imagine that a loose connection, corroded connection or frayed cable restricts current flow through the starter ground path. Techs often describe the condition as a bad ground. Remember that a bad starter ground may cause a variety of weird – perhaps intermittent – electrical symptoms.
Furthermore, a badly restricted ground may force starter current to seek another route back to the battery. This alternative path could take the current through components such as a clutch cable, floor shift cable, throttle cable, speedometer cable, etc. One potential clue is a burned cable housing and/or seized cable. Another is repeated cable failure with no obvious causes. Among other clues is a badly burned or blistered body ground strap or ground wire.
RECOMMENDED EQUIPMENT
First, reaching a starter often requires two steps – raising the vehicle on a lift and removing the splash shield under the engine. Be patient. Starter access tends to be poor and has been that way for many years.
Second, I recommend using a professional-grade digital voltmeter. This breed of meter has become a mainstay of modern automotive diagnosis. Plus, it usually contains at least two very practical features: Automatic scale ranging (auto-range) as well as minimum/maximum (MIN/ MAX) capture. As its name suggests, the auto-range feature saves you the guesswork of choosing the proper voltage scale for this ground test.
Meanwhile, enabling the MAX function greatly simplifies this test – as well as many other voltage measurements on a vehicle. In this situation, the MAX feature captures and remembers the voltage drop measurement while you’re cranking the engine. At the very least, using MAX means you don’t have to watch the meter during the test.
Third, you need adequate voltmeter test leads and alligator clips. Remember that you must connect the voltmeter between the negative battery terminal and the starter housing. This step could require test leads that are longer than those that came with your digital voltmeter.
You also may need a large alligator clip in order to get a good, reliable grip on the starter housing (Figure 1). Sometimes it’s difficult – if not impossible – to do this with the somewhat small alligator clips that came with the voltmeter. Years ago, I invested in larger alligator clips for test situations such as this one.
TRADITIONAL PROCEDURE
Okay, suppose you want to verify that a starter is thoroughly grounded. For the sake of this very brief discussion, I will assume that you already tested the battery and recharged or replaced it as needed.
First, safely disable the vehicle’s spark or fuel so the engine won’t start during this brief cranking test. The simplest way to do this varies from one vehicle to another. It may be as easy as pulling an ignition fuse, injector fuse, fuel pump relay, etc.
Next, set the meter to auto-range, DC volts and activate the MAX function. Securely connect the negative voltmeter lead to the negative battery post; firmly connect the other test lead to the starter housing (Figure 1).
Crank the engine for approximately five seconds. The meter will display the voltage drop across the entire starter ground circuit (Figure 4). A practical guideline is that the drop should measure 0.50 volt or less. The lower the measurement is, the better the condition of the ground circuit.
I first learned this cranking voltage drop procedure back in 1976; I have been practicing it since then. For one thing, practice helps. The more often you perform the test, the greater your confidence in it. For another, it is not uncommon to measure a starter ground voltage drop of 0.20 to 0.25 volt on a healthy vehicle (Figure 4).
Experience has shown that a failing starter ground usually measures substantially more than our working limit of 0.50 volt. When the voltage drop is excessive, there is an electrical restriction somewhere between the starter housing and the negative battery post. Potential restrictions include problems such as a loose, corroded, frayed or undersized negative battery cable.
Suppose the voltage drop is excessive. If it is, keep the one test lead securely on the negative battery post. Then move the other voltmeter lead back – along the ground path – toward the negative battery post. Move the test lead one section of the ground circuit at a time; repeat the cranking test each time. When the voltage drop measures normal again, you have reached a healthy section of the circuit.
Some techs are curious about the starter-to-engine or starter-to-transmission mating surfaces. I have checked the cranking voltage drop across these surfaces: Typically, it has measured less than 0.10 volt (Figure 3). And that ain’t much, folks!
Finally, don’t fret if you see a minus sign (-) on the meter reading. This just means that you reversed the test leads. Thankfully, this oversight does not harm a digital meter during a voltage measurement. And reversed test leads do not affect the accuracy of the voltage reading.
HEARSAY VERSUS MEASUREMENTS
Some techs have warned me that two seemingly harmless steps would harm a starter ground. The first was installing a painted starter; the second was applying anti-seize lubricant to the threads of the starter bolts. I was surprised because these steps had never caused me any trouble in the past.
The techs who practiced these precautions have said they got the information “on good authority.” But they have not verified them with cranking voltage drop tests. To me, untested opinions are hearsay – period. However, the warnings did spur me to double-check my own work.
Over the last eight years or so, I have had to replace several Honda and Toyota starters. I treated each job as an experiment. First, I carefully cleaned the starter mounting flange on each car’s bellhousing. Then I patiently sprayed several layers of paint onto that flange – as well as on the mounting flange of each replacement starter (Figure 2). I let the paint dry overnight.
Second, I cleaned the threads of the starter bolts and put a light film of anti-seize lubricant on them (Figure 5). Then I installed each starter and performed the same cranking ground test I described a moment ago.
The cranking voltage drop measurement on these jobs never exceeded 0.22 volt. Matter of fact, the test results on the last two Honda starter jobs measured 0.19 volt and 0.17 volt, respectively. For one thing, these unquestionably are excellent test results. For another, these readings strongly suggest that paint and anti-seize are non-issues on starter grounds. So, when all is said and done, testing and measuring beats guessing. Believe the measurement.













