Reduced Engine Power Limp Mode
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3rd Gear
Joined: Apr 2024
Posts: 3
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From: california
Reduced Engine Power Limp Mode
I have a 99 auto base c5 I've been having a reduced power issue for about 6 months now lately its happened pretty often I've tried replacing the TPS sensor, throttle body, tac module and battery its now a yellow top optima battery I've done all while trying to avoid reintroducing new bad parts, done live tests while driving the car 99% of the time the sensors show theyre within a 1-2% difference on throttle positions then suddenly read a 30% to 120% reading when the limp jumps on at times. The codes I've had from the start were 10-PCM p1516 H, p1515 H, p1221 H, p1120 H 28-PCM c1278 H
the focused reoccurring codes I've noticed are those of the PCM (p1515, p1221) the issue happens in both dry and wet climates, during redlight idles I've noticed the car starts to get more and more jittery over a few days before it decides to jump into the limped power reduction mode the second it gets under 500rpm it ***** the bed ive noticed to this day atleast from my own research they're isn't really any after market support for these parts would prefer not to throw money at a temp resolution if there's a way to completely replace the system with a newer year that has support that would be ideal if worth if not any advice or further questions helps, thank you.
the focused reoccurring codes I've noticed are those of the PCM (p1515, p1221) the issue happens in both dry and wet climates, during redlight idles I've noticed the car starts to get more and more jittery over a few days before it decides to jump into the limped power reduction mode the second it gets under 500rpm it ***** the bed ive noticed to this day atleast from my own research they're isn't really any after market support for these parts would prefer not to throw money at a temp resolution if there's a way to completely replace the system with a newer year that has support that would be ideal if worth if not any advice or further questions helps, thank you.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,615
Likes: 4,063
From: Cape Coral, Florida
My advise to you is take the car to a shop that uses a scope...a scan tool sometimes will not see those quick voltage drop outs due to its refresh rate being slow...a scope will take millions of voltage samples per second and will not miss that drop out...I'd also "wiggle check" the TPS wiring.
Tech Contributor
Joined: Jan 2007
Posts: 19,465
Likes: 1,167
From: Dyer, IN
I have a 99 auto base c5 I've been having a reduced power issue for about 6 months now lately its happened pretty often I've tried replacing the TPS sensor, throttle body, tac module and battery its now a yellow top optima battery I've done all while trying to avoid reintroducing new bad parts, done live tests while driving the car 99% of the time the sensors show theyre within a 1-2% difference on throttle positions then suddenly read a 30% to 120% reading when the limp jumps on at times. The codes I've had from the start were 10-PCM p1516 H, p1515 H, p1221 H, p1120 H 28-PCM c1278 H
the focused reoccurring codes I've noticed are those of the PCM (p1515, p1221) the issue happens in both dry and wet climates, during redlight idles I've noticed the car starts to get more and more jittery over a few days before it decides to jump into the limped power reduction mode the second it gets under 500rpm it ***** the bed ive noticed to this day atleast from my own research they're isn't really any after market support for these parts would prefer not to throw money at a temp resolution if there's a way to completely replace the system with a newer year that has support that would be ideal if worth if not any advice or further questions helps, thank you.
the focused reoccurring codes I've noticed are those of the PCM (p1515, p1221) the issue happens in both dry and wet climates, during redlight idles I've noticed the car starts to get more and more jittery over a few days before it decides to jump into the limped power reduction mode the second it gets under 500rpm it ***** the bed ive noticed to this day atleast from my own research they're isn't really any after market support for these parts would prefer not to throw money at a temp resolution if there's a way to completely replace the system with a newer year that has support that would be ideal if worth if not any advice or further questions helps, thank you.
Tech Contributor
Joined: Jan 2007
Posts: 19,465
Likes: 1,167
From: Dyer, IN
I guess I should have been more specific. You need a multimeter to evaluate the resistance in the wiring between connectors.
