2002 3.8 Bird - Reduced Engine Power - Lots of Codes
03-14-2020, 06:15 PM
#1
2002 3.8 Bird - Reduced Engine Power - Lots of Codes Hi All
I have a 2002 3.8 Firebird that suddenly went into reduced power mode after a one hour trip.
100% stock, intake gaskets already replaced (common issue), battery and alternator are fine.
Fires right up, then a few feet down road the mode kinks in.
It will accel slowly and run mostly fine, just slow like Im not giving throttle.
Codes are;
P1518 - Throttle Actuator Control (TAC) Module Serial Data Circuit
P0155 - Heated Oxygen Sensor (HO2S) heater circuit Bank 2 Sensor 1
P0404 - EGR fault - Ill likely try cleaning, but know this wouldnt be the source of limp mode as Ive had many of this code between Fbodies
U1000 - Class 2 data link malfunction
P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) - IIRC I have a lower degree stat
C0240 - Powertrain Control Module Traction Control Not Allowed
Appreciate any help
I have a 2002 3.8 Firebird that suddenly went into reduced power mode after a one hour trip.
100% stock, intake gaskets already replaced (common issue), battery and alternator are fine.
Fires right up, then a few feet down road the mode kinks in.
It will accel slowly and run mostly fine, just slow like Im not giving throttle.
Codes are;
P1518 - Throttle Actuator Control (TAC) Module Serial Data Circuit
P0155 - Heated Oxygen Sensor (HO2S) heater circuit Bank 2 Sensor 1
P0404 - EGR fault - Ill likely try cleaning, but know this wouldnt be the source of limp mode as Ive had many of this code between Fbodies
U1000 - Class 2 data link malfunction
P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) - IIRC I have a lower degree stat
C0240 - Powertrain Control Module Traction Control Not Allowed
Appreciate any help
03-15-2020, 09:06 AM
#3
Have you disconnected the wires going into the PCM ever? There was a TSB requiring that the PCM seal connector be replaced whenever it is removed to prevent water going in and corroding the pins. When that happens, the whole sensor world goes haywire like this.
Another common cause is when folks replace their exhaust and a bundle of wires melts on the new tubes. ... Or when a rodent gets into the engine compartment and decides to have a snack on wire insulation.
Regardless, I would start by taking an inventory of those sensors and tracing the bundles they pass through and see if you can find any common damage to a wire harness.
Another common cause is when folks replace their exhaust and a bundle of wires melts on the new tubes. ... Or when a rodent gets into the engine compartment and decides to have a snack on wire insulation.
Regardless, I would start by taking an inventory of those sensors and tracing the bundles they pass through and see if you can find any common damage to a wire harness.
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andrewss (04-30-2020)
03-15-2020, 08:53 PM
#4
TECH Veteran
iTrader: (14)
Definitely check the grounds wouldn't be the first time that out one in limp.mode. v6 cars are drive by wire so could be either you peddle or the TB, but the other codes associated are a bit troubling
More likely a ground issue or water in connectors or fuse/relay. Check pcm connection if you open. It up and see either water or white oxidation most likely you have water issues
More likely a ground issue or water in connectors or fuse/relay. Check pcm connection if you open. It up and see either water or white oxidation most likely you have water issues
03-15-2020, 09:42 PM
#5
Thanks for the tips everyone!
I have never pulled the PCM connections, but thats not to say previous owner hasnt.
Ill look at that tomorrow afternoon. I have some Deoxit if theres oxidation.
Ive looked and touched all the wire looms I could see and/or reach.
All seem fine.
Will update
I have never pulled the PCM connections, but thats not to say previous owner hasnt.
Ill look at that tomorrow afternoon. I have some Deoxit if theres oxidation.
Ive looked and touched all the wire looms I could see and/or reach.
All seem fine.
Will update
(I recall they run $20-30) You may still want to do this at some point, but I would save it for last.
04-06-2020, 10:32 PM
#7
Updates:
So I looked at all the grounds I could find, even took a set of cables and grounded the TB to the neg terminal (not sure if that would even help).
Checked the PCM connectors. Most definitely the cleanest newest looking items on the whole car.
Pulled intake plastics and looked at TB blade. It does respond to the pedal press, tho not much and continues to run like crap (or worse with pedal press).
Finally got my own scanner in and checked codes again. I only have the P1518 code.
I also looked at live data for the throttle position; 17.64% and never changes, at all.
What next?
So I looked at all the grounds I could find, even took a set of cables and grounded the TB to the neg terminal (not sure if that would even help).
Checked the PCM connectors. Most definitely the cleanest newest looking items on the whole car.
Pulled intake plastics and looked at TB blade. It does respond to the pedal press, tho not much and continues to run like crap (or worse with pedal press).
Finally got my own scanner in and checked codes again. I only have the P1518 code.
I also looked at live data for the throttle position; 17.64% and never changes, at all.
What next?
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04-07-2020, 08:03 PM
#8
That's the module that controls the cruise control. There's a very long procedure to test the circuit for it to rule it out as being defective, or not - but I would start there. The Factory Service Manual has the procedure for DTC1518, which you can also get on the 3 day Service Information subscription here: https://www.acdelcotds.com/subscriptions
You should see the TPS values change as the throttle body moves. If not, that may be the first thing to go after. A lot of times the scanner refresh rate is not fast enough to pick up subtle changes in the sensors readings, but you should be able to see it change a lot when it goes wide open.
You should see the TPS values change as the throttle body moves. If not, that may be the first thing to go after. A lot of times the scanner refresh rate is not fast enough to pick up subtle changes in the sensors readings, but you should be able to see it change a lot when it goes wide open.
04-07-2020, 08:18 PM
#9
11 Second Club
iTrader: (3)
Updates:
So I looked at all the grounds I could find, even took a set of cables and grounded the TB to the neg terminal (not sure if that would even help).
Checked the PCM connectors. Most definitely the cleanest newest looking items on the whole car.
Pulled intake plastics and looked at TB blade. It does respond to the pedal press, tho not much and continues to run like crap (or worse with pedal press).
Finally got my own scanner in and checked codes again. I only have the P1518 code.
I also looked at live data for the throttle position; 17.64% and never changes, at all.
What next?
So I looked at all the grounds I could find, even took a set of cables and grounded the TB to the neg terminal (not sure if that would even help).
Checked the PCM connectors. Most definitely the cleanest newest looking items on the whole car.
Pulled intake plastics and looked at TB blade. It does respond to the pedal press, tho not much and continues to run like crap (or worse with pedal press).
Finally got my own scanner in and checked codes again. I only have the P1518 code.
I also looked at live data for the throttle position; 17.64% and never changes, at all.
What next?
That's my home town and haven't been back since the late 80's. Is the lake still the Friday night hangout?
I can still remember the time I drove over the levee in my 77 Camaro only to see the cops waiting to bust our asses on the other side!
04-07-2020, 10:46 PM
#10
That's the module that controls the cruise control. There's a very long procedure to test the circuit for it to rule it out as being defective, or not - but I would start there. The Factory Service Manual has the procedure for DTC1518, which you can also get on the 3 day Service Information subscription here: https://www.acdelcotds.com/subscriptions
You should see the TPS values change as the throttle body moves. If not, that may be the first thing to go after. A lot of times the scanner refresh rate is not fast enough to pick up subtle changes in the sensors readings, but you should be able to see it change a lot when it goes wide open.
You should see the TPS values change as the throttle body moves. If not, that may be the first thing to go after. A lot of times the scanner refresh rate is not fast enough to pick up subtle changes in the sensors readings, but you should be able to see it change a lot when it goes wide open.
I tested the TPS reading again. Held throttle and never changed value, just ran worse.
I also checked FP. Was around 45 on/off and in running. A couple times went to dead zero when turning off engine from a running state.
04-08-2020, 07:56 AM
#12
You have two throttles on the car. One is controlled by the cable connected to the pedal you press with your foot and the second is controlled by the cable connected to the cruise control. If that module is going haywire, odd things could happen, but...
Your TPS is probably the first thing to chase down. You could be getting a cruise control code if the computer doesn't see the throttle response (from the sensor) that it would expect from actuating. (...or it may not be that smart) Regardless, the TPS is pretty easy to trace with a voltmeter. More often than not, people have a TPS wiring problem vs. an actual problem with the sensor - but the sensors do go bad. There are many videos on youtube about testing and diagnosing TPS circuits and a few good threads on this site, as well.
Your TPS is probably the first thing to chase down. You could be getting a cruise control code if the computer doesn't see the throttle response (from the sensor) that it would expect from actuating. (...or it may not be that smart) Regardless, the TPS is pretty easy to trace with a voltmeter. More often than not, people have a TPS wiring problem vs. an actual problem with the sensor - but the sensors do go bad. There are many videos on youtube about testing and diagnosing TPS circuits and a few good threads on this site, as well.
04-08-2020, 09:39 AM
#13
TECH Veteran
iTrader: (14)
You have two throttles on the car. One is controlled by the cable connected to the pedal you press with your foot and the second is controlled by the cable connected to the cruise control. If that module is going haywire, odd things could happen, but...
Your TPS is probably the first thing to chase down. You could be getting a cruise control code if the computer doesn't see the throttle response (from the sensor) that it would expect from actuating. (...or it may not be that smart) Regardless, the TPS is pretty easy to trace with a voltmeter. More often than not, people have a TPS wiring problem vs. an actual problem with the sensor - but the sensors do go bad. There are many videos on youtube about testing and diagnosing TPS circuits and a few good threads on this site, as well.
Your TPS is probably the first thing to chase down. You could be getting a cruise control code if the computer doesn't see the throttle response (from the sensor) that it would expect from actuating. (...or it may not be that smart) Regardless, the TPS is pretty easy to trace with a voltmeter. More often than not, people have a TPS wiring problem vs. an actual problem with the sensor - but the sensors do go bad. There are many videos on youtube about testing and diagnosing TPS circuits and a few good threads on this site, as well.
3.8's are drive by wire, could be at the throttle body or the sensor on the pedal. ill look when I get home i have my old 3.8 assembly in the garage I cant remember if any of it is exposed where it could use a good cleaning or not on the pedal side.
04-08-2020, 10:03 AM
#14
11 Second Club
iTrader: (3)
3800 Series II's are drive by wire and it sounds like the car is running in limp mode. Not sure if the fuel pressure is an issue or not but that could cause running and idle issues.
Get yourself a code scanning tool and make sure all of your connections are good and that you have a healthy battery then go drive it around to get a drive cycle on the car in order for the computer to clear the codes.
Get yourself a code scanning tool and make sure all of your connections are good and that you have a healthy battery then go drive it around to get a drive cycle on the car in order for the computer to clear the codes.
04-08-2020, 10:13 AM
#15
11 Second Club
iTrader: (3)
P1518
Have you replaced the TAC?
Have you replaced the TAC?
04-09-2020, 07:32 AM
#16
04-09-2020, 10:37 AM
#17
TECH Veteran
iTrader: (14)
Your not wrong, a good scan tool should tell you whats going on if its part of the pedal/tps/TB system. Either of those 3 being out of whack would send you into limp mode. the most basic thing to do which I think you already did. Is have it on switched ignition and press the petal full down and check to to see if the TB reacts to the commands. Which reading through I see you are not getting full actuation, im curious was the reduced power light on during that test? Might prohibit the tb from opening all the way if the system was still in "limp mode".
From there im not quite sure the feedback loop, but essentially the pedal is a sweeping resistor that correlates to a Throttle body positon for the TB blade's actuator. If the improper resistance is give the TB wouldnt open fully (or if you put a TPS sensor on the wrong way that could cause similar issues though I do think there is a d shape on the shaft that prevents this). In Theory the TPS confirms the TB acutator and the pedal placement are correct, so if your petal went down and the TB didnt open (TPS would see this) that would put you into limp mode as well.
is there are a lot of carbon build up in the Throttle Body? could just need a good cleaning and the actuator may be having some trouble fully opening.
If you have access to a good scan tool where you view the values coming from the petal, or fully actuate the TB via the scan tool and see if it can go full open, that would narrow it down for you. Im not sure if a hanes manual would give you the proper values and which pins so you could just probe it with a multimeter or not.
Give some of this stuff a try or if you have access to some spare parts try swapping the TB out, and or pedal. TPS sensors are pretty cheap as well by comparison you could try that also.
From there im not quite sure the feedback loop, but essentially the pedal is a sweeping resistor that correlates to a Throttle body positon for the TB blade's actuator. If the improper resistance is give the TB wouldnt open fully (or if you put a TPS sensor on the wrong way that could cause similar issues though I do think there is a d shape on the shaft that prevents this). In Theory the TPS confirms the TB acutator and the pedal placement are correct, so if your petal went down and the TB didnt open (TPS would see this) that would put you into limp mode as well.
is there are a lot of carbon build up in the Throttle Body? could just need a good cleaning and the actuator may be having some trouble fully opening.
If you have access to a good scan tool where you view the values coming from the petal, or fully actuate the TB via the scan tool and see if it can go full open, that would narrow it down for you. Im not sure if a hanes manual would give you the proper values and which pins so you could just probe it with a multimeter or not.
Give some of this stuff a try or if you have access to some spare parts try swapping the TB out, and or pedal. TPS sensors are pretty cheap as well by comparison you could try that also.
04-09-2020, 10:23 PM
#18
IIRC, TPS is not serviceable on the 3.8, you have to replace the whole throttle body. And they have become very hard to find new.
My guess is this is what you're going to come down to on your car. It happened on one of my son's V6, but we had a spare motor and just swapped it for the fix.
My guess is this is what you're going to come down to on your car. It happened on one of my son's V6, but we had a spare motor and just swapped it for the fix.
04-16-2020, 12:28 AM
#19
Ive got the kick panel off, and it is not exposed and looks very clean.
3800 Series II's are drive by wire and it sounds like the car is running in limp mode. Not sure if the fuel pressure is an issue or not but that could cause running and idle issues.
Get yourself a code scanning tool and make sure all of your connections are good and that you have a healthy battery then go drive it around to get a drive cycle on the car in order for the computer to clear the codes.
Get yourself a code scanning tool and make sure all of your connections are good and that you have a healthy battery then go drive it around to get a drive cycle on the car in order for the computer to clear the codes.
The principle should still be the same with a cable at the throttle body actuating the pedal part of the circuit. If there are two TPS signals, the scan tool should be able to show that. With someone pressing the pedal, someone observing the throttle body and observing the scan readings, it should be easy to start isolating where the problem is.
From what I seen, the TB did open, but not much. Reading was still the same the entire time. No new codes.
Your not wrong, a good scan tool should tell you whats going on if its part of the pedal/tps/TB system. Either of those 3 being out of whack would send you into limp mode. the most basic thing to do which I think you already did. Is have it on switched ignition and press the petal full down and check to to see if the TB reacts to the commands. Which reading through I see you are not getting full actuation, im curious was the reduced power light on during that test? Might prohibit the tb from opening all the way if the system was still in "limp mode".
From there im not quite sure the feedback loop, but essentially the pedal is a sweeping resistor that correlates to a Throttle body positon for the TB blade's actuator. If the improper resistance is give the TB wouldnt open fully (or if you put a TPS sensor on the wrong way that could cause similar issues though I do think there is a d shape on the shaft that prevents this). In Theory the TPS confirms the TB acutator and the pedal placement are correct, so if your petal went down and the TB didnt open (TPS would see this) that would put you into limp mode as well.
is there are a lot of carbon build up in the Throttle Body? could just need a good cleaning and the actuator may be having some trouble fully opening.
If you have access to a good scan tool where you view the values coming from the petal, or fully actuate the TB via the scan tool and see if it can go full open, that would narrow it down for you. Im not sure if a hanes manual would give you the proper values and which pins so you could just probe it with a multimeter or not.
Give some of this stuff a try or if you have access to some spare parts try swapping the TB out, and or pedal. TPS sensors are pretty cheap as well by comparison you could try that also.
From there im not quite sure the feedback loop, but essentially the pedal is a sweeping resistor that correlates to a Throttle body positon for the TB blade's actuator. If the improper resistance is give the TB wouldnt open fully (or if you put a TPS sensor on the wrong way that could cause similar issues though I do think there is a d shape on the shaft that prevents this). In Theory the TPS confirms the TB acutator and the pedal placement are correct, so if your petal went down and the TB didnt open (TPS would see this) that would put you into limp mode as well.
is there are a lot of carbon build up in the Throttle Body? could just need a good cleaning and the actuator may be having some trouble fully opening.
If you have access to a good scan tool where you view the values coming from the petal, or fully actuate the TB via the scan tool and see if it can go full open, that would narrow it down for you. Im not sure if a hanes manual would give you the proper values and which pins so you could just probe it with a multimeter or not.
Give some of this stuff a try or if you have access to some spare parts try swapping the TB out, and or pedal. TPS sensors are pretty cheap as well by comparison you could try that also.
From my understanding, the code is the PCM communication issue with the TAC module, and that is the pedal side. Tho I have yet to see any of the fixes actually be this. I have an electronic copy of the FSM and found the procedures for testing it. Tho it seems it will be VERY hard to get under the dash to do so.
As for the TPS sensor, it isnt replaceable. Has to be the whole TB, and all I can find of those are used and expensive.
IIRC, TPS is not serviceable on the 3.8, you have to replace the whole throttle body. And they have become very hard to find new.
My guess is this is what you're going to come down to on your car. It happened on one of my son's V6, but we had a spare motor and just swapped it for the fix.
My guess is this is what you're going to come down to on your car. It happened on one of my son's V6, but we had a spare motor and just swapped it for the fix.
Last edited by nimrod.sixty9; 04-16-2020 at 12:54 AM.
04-16-2020, 06:40 AM
#20
I dunno. I was pointing out that in order to do a complete test of a sensor at the throttle body, you would need to be standing there and observing it. This generally takes two people; one on the pedal and one in the engine compartment. Another nice feature is having a scanning tool that snakes all the way back to the engine compartment. (Not all do.)