QuestionHi Roland, I bought a GM code reader. The codes I got were 23, 24, 42. I have a 1984 Grand Prix LE, 305 V8. The code book mentions a lot of things that could set off the engine check light, but which would be more likely for it to happen only when going over 55 mph?
John B.
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Followup To
Question -
My engine warning light comes on when I go over 55 MPH. An autoshop told me it was the speed sensor. The speedometer works fine, would it still be the speed sensor? Will it harm the engine if it's not fixed soon?
John B
Answer -
Hi John,
If the shop based their statement on an actual readout of your engine controller then I would be more certain in my answer. But just in case, you can verify whether this is true. Try using the ignition key: turn it "on-off-on-off-on" and leave it "on" (doing this quickly, no longer than 5 seconds). Then watch the 'check engine' light to begin flashing, then pause, flashing, pause, etc. Count the number of flashes before each pause and keep track of the numbers. Repeat the readout and verify the counts are correct. Then group them in pairs in the order that they came out, thus forming two digit numbers. You may notice that the pause is shorter between the digits of a given number, and longer between the numbers themselves. Then send me a 'follow-up' question telling me the results of your readout. By the way, 55 will be the last number (two groups of 5 flashes each) and that is the code for "end of readout". The code for a problem with the sensor is 15.
There is also an essay on fault codes at the site:
http://www.allpar.com/fix/codes.html
which gives the meaning of the code numbers. But then you need to get specific info for what exactly might be the diagnostic tests or parts to replace to complete the repair.
I don't believe any problem will develop that hurts the engine from a speed sensor issue.
When you write back with the results of your attempt, tell me what year, model, engine, and transmission that you have so I can give you more accurate advice.
Roland
AnswerHi John,
That is an interesting question as I am unaware if the code numbers are identical between the GM and Chrysler vehicles.
Assuming that they are, the 23 has to do with the engine coolant temp sensor circuit so you might check the wiring to that and also verify that the resistance of the sensor is in the range of 700 to 1,000 ohms when the engine is up to operating temp. (and 7,000 to 14,000 ohms when cold). Sometimes the engine light will come on if the sensor thinks the engine is not warming up after a some number of minutes of operation, even though it is. How is you cooling system operating, according to the temp gauge if you have one?
24 has to do with the throttle position sensor, again this could be wiring as it is usually in a very hot area so check that the wiring to it isn't melted. Then you could check the variable resistances between 2 of the 3 possible combinations you can choose to read across the 3 pins of the sensor (the other combination will just be a fixed resistance regardless of the throttle position). The resistance across those 2 configurations should vary smoothly with the motion of the throttle (but inversely to oneanoter) with no discontinuity in the reading. If there is, then replace the sensor.
The 42 has to do with the autoshutdown relay and I don't see how that is related to going over 55. If there was something wrong I would think the engine would die, unless perhaps the circuit has been tampered with and is not able to actually shut down the engine when it needs to (i.e. in the case of an accident when the key is in the run position and the engine stops turning over. It is supposed to shut down the fuel pump and spark for fire prevention.)
I would be curious to know if the definition that you got for these codes is identical.
Roland
