check engine light on but cant pull any codes
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check engine light on but cant pull any codes
My check engine light is on and as i go to use my obd1 scan tool it wont do anything i know the tool works bc i then tried it on another one of my cars. I try to reset the computer by disconnecting the battery and it just comes right back on. Any ideas?
Fleet Owner
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From: Kentucky
ST0 and STI are the connectors your scanner plugs into. It may have worked last week, but obviously it is not wotking this week. You already verified your scanner works on a different vehicle. The next step is to clean the connectors.
Some other info to consider: FordFuelInjection.com - No Codes?
Some other info to consider: FordFuelInjection.com - No Codes?
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ok how can i clean the connectors. And some more info is when i press the test mode buttom it sounds like its working but not giving any codes. Im trying to fix my iac problem but cant get any codes. How do i know if my pcm is going bad.
Fleet Owner
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From: Kentucky
I use a small screwdriver and electronic contact cleaner. If all else fails try using this method to check for codes: Ford Fuel Injection » How To Run a Self-Test
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ok ill do tha tbut when my code reader starts the test i can hear the relays and fuel pump but no codes.
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Fleet Owner
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From: Kentucky
That tells me STI is getting grounded which in turn triggers the PCM to start the KOEO tests. I suspect the problem is the Data Link connections on ST0 are corroded or some other reason to have a bad connection.
Last edited by rla2005; Mar 16, 2011 at 06:04 PM. Reason: Swapped ST1 and ST0 description
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ok got it figured out i guess i had the data plug plugged in wrong. I got the codes codes 121 which is somthing about throttle voltage higher or lower than normal. Could his be related to why my truck idles high when iac is plugged in and runs fine when not plugged in. And a 542 which is a fuel pump relay but my front one works so i dont see why that code is coming on unless since my rear one doesnt.
Fleet Owner
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From: Kentucky
Code 121/bad TPS can cause a high idle issue. Very common, actually. I always measure them before pronouncing them dead. Code 542 could be a KOEO code or read from CM. If it is from CM it was from a previous event. An open in the fuel circuit or open windings in the fuel pump can cause this code if that tank gets selected.
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Ok you been very help. Do you know a link or can you explian how to check voltage to the tps i have a volt meter i know for most fords it should be at 1 volt at idle. So for my engine to idle at 2000 it must be at a high voltage. Mabe it just needs ajusted and i also dont know how to do that.
Fleet Owner
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From: Kentucky
There typically is no adjustment for the TPS on these trucks. Some have tried to swap on one with slotted attachment screws. Anything between 0.6-1.0VDC with the throttle closed is what you are looking for.
There is ZERO value in trying to set a TPS to the mythical value of 0.99 VDC with the throttle closed. The PCM has a ratchet function built-in, it is always looking for the lowest value it sees then adjusts accordingly.
The most common scenario is a dirty wiper inside the TPS. The PCM "sees" varying output values because of the noisy signal. That is why I suggested to check the static value then run the throttle open and closed a few times while watching the meter. An old analog style meter is best, but it can be done with a DVM just as well if you watch closely.
Another helpful bit of info from Ryan at Ford Fuel Injection » Throttle Position Sensor (TPS)
More helpful info from my buddies at FullSizeBronco.com - Ultimate Throttle Position Sensor (TPS) Thread
There is ZERO value in trying to set a TPS to the mythical value of 0.99 VDC with the throttle closed. The PCM has a ratchet function built-in, it is always looking for the lowest value it sees then adjusts accordingly.
The most common scenario is a dirty wiper inside the TPS. The PCM "sees" varying output values because of the noisy signal. That is why I suggested to check the static value then run the throttle open and closed a few times while watching the meter. An old analog style meter is best, but it can be done with a DVM just as well if you watch closely.
Another helpful bit of info from Ryan at Ford Fuel Injection » Throttle Position Sensor (TPS)
More helpful info from my buddies at FullSizeBronco.com - Ultimate Throttle Position Sensor (TPS) Thread
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as i was about to remove the tb i noticed a rubber hose that goes into the side of it. It was really brittle as i barley pulled on it it broke. Is this a vac line? If so this could be the vac line that could of caused the high idle.
Fleet Owner
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From: Kentucky
That is probably for the purge canister. Yes it is a vacuum line that could be a vacuum leak if it is degraded or broke. Is it enough to cause a high idle? perhaps.
This leads me to the issue of the integrity of all the vacuum lines. Check the TPS voltage with the throttle closed. Then start taking a look at all of the vacuum lines and reservoirs. These trucks are old and have suffered through multiple owners. Some were more kind than others.
This leads me to the issue of the integrity of all the vacuum lines. Check the TPS voltage with the throttle closed. Then start taking a look at all of the vacuum lines and reservoirs. These trucks are old and have suffered through multiple owners. Some were more kind than others.