When All Else Fails, It's Time to Test

Posted 1/13/2010
By Brad Davis

The technician started by checking our website for common no-start issues. He saw the crankshaft position (CKP) sensor was a common failure item for no spark. He installed a new CKP sensor (without checking it). Statistically, this would have fixed the problem, but in this case it did not. Then the technician installed a new camshaft position sensor. When that didn't work, he installed a new engine control module (ECM). That was strike three. Now it was time to perform some testing procedures. When checking the new sensor's resistance, the technician noted it was out of specification so he installed another new sensor. No help.

This is when the technician called our repair hotline. I asked if he had looked at the CKP sensor using a labscope. He had not checked it since he didn't know what a known good pattern should look like. I faxed a picture of a known good CKP sensor signal to him.

When he checked the pattern, it showed that the voltage output was lower than normal. Then I asked the technician to check the resistance reading of the sensor. It was at 860 ohms, which is out of range compared to Hyundai's specification of 500 ohms. I suggested the technician install a sensor directly from Hyundai since his replacement was more than 350 ohms out of spec. The new sensor from Hyundai read 800 ohms also. Obviously the spec in the book is wrong. The technician installed the new sensor but the engine still would not start.

I asked him to check the CKP sensor using his lab scope again and to compare it to the known good pattern. It still looked to be outputting low voltage. We inspected the crankshaft reluctor wheel, and it was tight with no scratches or marring.

When I had him verify that two "O" rings were not stuck in the mounting hole and that the sensor was pulled flush against the engine block when being tightened, he noted that when tightening the single mounting bolt on the sensor, the sensor body would pull in and then cock a little in the bore. The technician loosened the sensor and tapped on it to straighten out the sensor. When he tightened the mounting bolt, he made sure to lightly tap on the sensor to allow the sensor to pull all the way into the mounting hole. The technician cranked the engine and it started immediately!

The problem was that the sensor was not going into the hole in the block completely. The sensor signal looked perfect but the signal voltage output was too low so the computer could not recognize the signal. If you replace one of these sensors, make sure it mounts flush to the block before you start replacing other parts.

Brad Davis is an Identifix Asian specialist. He is a certified Toyota master and ASE master with L1 certification.

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