Starter is a likely culprit
Q I'm hoping you can help me with my 2001 Blazer. It has failed to start on a dozen or so occasions. It will make no sound when I turn the key. About two or three different times, someone did something down at the starter and it started. Another time, someone jiggled the battery cables and it started. My mechanic replaced the starter relay, but that didn't help. It has 160,000 miles. I'm very frustrated with this problem as no one seems to be able to fix it.
A I can appreciate your frustration as an intermittent no-start condition can place you in an inconvenient or dangerous situation. Your description of no sound helps pin this down as a no-crank starting problem as opposed to a cranking no-start (run) issue. Possible culprits include the battery, battery terminals, ignition switch, park-neutral switch, starter relay, wiring to starter and starter connections, and the starter itself. Let's wade through these and rule out as many as possible. You'll need to endure just one more episode to get to the bottom of this.
It sounds like the battery is OK, as you don't mention needing to jump-start the Blazer. To be sure, during an unsuccessful cranking attempt, turn on the headlights. If they remain bright as the key is tried, the battery and battery cable terminals are OK.
Next are the ignition and park-neutral switches. During an unsuccessful cranking episode, try working the key start position by rotating the key less, more etc. Same goes for the park-neutral switch, try selecting neutral, wiggling the shift lever, exploring the edges of both the park and neutral shifter detents as the key is held to the crank position. If even brief cranking or noises are heard, the wiggled switch is likely the problem.
Your starter relay lives in a very convenient, accessible location within the under-hood fuse box, a 5-inch square plastic black box with a knob-attached lid, under the hood on the left-upper side. Try removing the cover and feeling the relay — a 1-inch square black cube, centered in the box - as a helper successfully cranks the engine. You'll feel a click. Now you know what to check for next time the Blazer fails to crank. If the relay fails to click during a no-start episode, the fault is likely within the ignition or park neutral switches, or a loose terminal at connector C-100 at the firewall. Since the relay is new and didn't fix the problem, I'll take a chance and rule it out as a likely culprit.
Now we'll close in for a solution: If during a no-crank episode the headlights do not dim and the relay clicks as the key is tried, the fault almost has to be within the starter. With 160,000 miles on the clock, the starter, if original, is on borrowed time. Its brushes are likely worn very short and may make only tentative contact with the armature. A swift smack to the starter can often induce the parts to work briefly — that may have been what was tried by the helpers. A loose electrical connection at the starter is also a possibility, but these are virtually impossible to access without removing the starter. If going to the trouble to do this, I'd renew it anyway.
Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at firstname.lastname@example.org; he cannot make personal replies.