“We’ve checked everything on this vehicle and it still stalls intermittently,” the shop owner said to me over the phone. It was a shop in St. Paul and I wasn’t about to travel to determine why a 2005 Malibu intermittently stalled.

“If you checked everything, then there is nothing left for me to check,” I said. “Tell me exactly what happens on this vehicle.”

“The customer said that it idles rough and stalls, and then it restarts with the Malfunction Indicator Light on and the Reduced Power Message on the dash. The customer shuts of the engine for about a minute and then restarts it. The MIL is still on but the vehicle is not in reduced power mode.”

“When does it stall?” I asked. “Going over bumps?”

“Sometimes, yes—sometimes it stalls going down a smooth road. Sometimes it stalls going around curves—in other words, road conditions don’t matter.”

I jotted that down. “What about ambient temperature? We have a roller coaster of temperatures going on—does it occur when it’s warm or cold outside?”

“It makes no difference,” Al, the shop owner, said.

“What about engine operating conditions,” I asked, “Does it stall during engine warm-up or when the engine is at normal operating temperature?”

“Yes,” the shop owner said, “in other words, it makes no difference.”

I wrote that down. “Does it stall at idle?”

“Sometimes it does, but sometimes it stalls driving down the road, too.”

Hmmm. The fault is obviously inconsistent.

“When it stalls, does it restart without a problem?”

“Every time,” Al replied.

“Did you get it to act up at the shop or on a road test?”

“Just one time, while the technician was pulling it inside. It did exactly what the customer said it did.”

I wrote that down. “Okay, did you do a good visual inspection, including checking all the fuses?”

“Yep—we also checked the fuses with both a test light and a voltmeter. They’re good.”

I wrote that down. “Did you record any fault codes?”

“Yep—there is a P1682, Ignition 1 Voltage Low, and a P2101, Throttle Actuator System Performance code. Every time the customer returns, those are the only two codes.”

That would help.

“What was done to repair it?”

“We put a new engine computer in the vehicle along with the 8-way F-Global terminal 150 Series terminal because we might have damaged it by backprobing it too much.”

“You said you put in a new computer; is it a remanufactured or brand new?”

“Well, it’s new to the Malibu,” Al said. “We got it from a salvage yard. It’s used.”

I rolled my eyes back. “Call me when you install a brand new, never-used-before computer, Al.”

I ended the call. I researched the two consistent fault codes, looking for a common denominator. In both cases, the diagnostics stated that the Electronic Temperature Control fuse should be checked with the key on, engine off, using a test light. The diagnostic stated that the engine computer should be replaced as a final step.

The following week Al called again to say that they put a brand new engine computer in the vehicle, programmed it and road tested the Malibu. The customer picked it up and brought it back to the shop because it stalled in exactly the same way.

“We even replaced the ETC fuse and it made no difference,” Al said. Everything checks out okay.”

“Of course you checked the grounds, right?”

“One of the first things we checked, of course. By the way, what is the difference between ground and reference low?”

The service manual instructed the technician to check the ETC fuse by using a test light and with the key on, engine off. “What did you say?”

“I always wanted to know the difference between reference low and ground,” Al said. I reread the service information about checking the fuse using a test light.

“Okay, Al,” I said, “this is what I want you to do to check that fuse correctly.”

Think about it and I will offer the solution in my next blog.

This is Jack McGinnis, HiTech Investigations, closing shop for the night.