Im at a loss...
Thread Starter
CF Beginner
Joined: Jul 2018
Posts: 3
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From: Northern California
Im at a loss...
Vehicle is a 2003 Chevy Suburban 1500 with the 5.3 vortec. Auto, 4x4 with 181,641 miles, not mine but my daughter's babysitter. Myself, I have been working on vehicles for a long time privately and I have many loyal customers with multiple vehicles and I stay extremely busy just by word of mouth alone, I don't advertise my shop.
On to the problem... Truck started to have issues with idle, high and rough surging idle in park or in gear. Showed code p0120. Cleared the code and cleaned the throttle body and checked tps connections and it then threw a code for the throttle actuator/position sensor. I replaced that and its pigtail and wires back 12". Immediately upon start up it threw the Reduced Engine Power on the cluster display and lost accelerator pedal response. So I "Hit the books" and began reading everything I could about the REP message and this ridiculous drive by wire system. I learned that GM sucks at grounding this generation of vehicles, so that was my next step. I located and cleaned the grounds under the drivers side door, behind the right and left cylinder head (which were said to be very difficult to get to, but I disagree) and cleaned up the grounds from bat neg to chassis and engine block. In doing so, I discovered that a rodent had chewed through 2 B+ wires at the fuse block, 2 wires coming from the TAC module located on the firewall, and a ground wire that ran to the ECM I believe. Upon further inspection of the fuse block and wires, the underside of the block was badly corroded outside and in and smelled of burned wiring. Wonderful... The TAC module also emitted a burned wire smell when I tapped on it. I theorized that this rat, spawned from satan himself, had chewed these wires causing a short and likely frying some modules when I moved some wires specifically to **** me off and lead me to an even stronger hatred for rats. SO, I proceeded to replace the TAC module, the accelerator pedal sensor, Fuse block, repaired/replaced all broken/chewed wires, replaced the ground strap and added an additional ground strap from the firewall to the block cause why not. Relocated the TPS/Actuator ground to a more convenient and clean location, cleaned the MAF sensor with some CRC cleaner and replaced the instrument cluster because it had lost the back lighting for PRND321 selection and had something going on with other lights which was, coincidentally happening before the DEP message. Checked the small fuse block by the drivers door, all wires I could get to behind the knee bolster and instrument cluster, wiring in the steering column and the ignition switch and pigtails.
Now after all of that, you would think it would be done right? You would be wrong... Upon initial start up, the truck ran great and throttle response was perfect. I was skeptical, so I took it for a test drive. Drove great. Parked it, shut it off and started it again a couple of times, then it threw the DEP message again with no accelerator response and codes p1518 (TAC to ECM signal circuit, not finding much information on this code) and p0220 (Throttle/Pedal Position Sensor/Switch "A" Circuit Malfunction) I cleared codes, and it fired right up, drove great again. stopped again, shut it off and started it back up no problem and drove home. Got to my driveway and shut it off, started it back up and it gave the DEP message again. I have double checked all grounds, wires and everything I can think of. It seems to be random, follows no pattern. Sometimes I can start and run it 20 times in a row with no DEP or codes before they set again. Sometimes it happens again and again, always the same 2 codes... P1518 and P0220. And every time they set, if I clear them the truck starts and runs great until it is shut off and restarted. My next step, I guess, is going to be taking it to the stealership and have them test the ECM and see if it is functioning properly. This truck is driving me crazy and I have too many other projects stacking up and a list of other client vehicles to get to. I have gotten a great deal of information from this forum site and am hoping someone can give me an idea what to do next aside of replacing the ECM. Help?
On to the problem... Truck started to have issues with idle, high and rough surging idle in park or in gear. Showed code p0120. Cleared the code and cleaned the throttle body and checked tps connections and it then threw a code for the throttle actuator/position sensor. I replaced that and its pigtail and wires back 12". Immediately upon start up it threw the Reduced Engine Power on the cluster display and lost accelerator pedal response. So I "Hit the books" and began reading everything I could about the REP message and this ridiculous drive by wire system. I learned that GM sucks at grounding this generation of vehicles, so that was my next step. I located and cleaned the grounds under the drivers side door, behind the right and left cylinder head (which were said to be very difficult to get to, but I disagree) and cleaned up the grounds from bat neg to chassis and engine block. In doing so, I discovered that a rodent had chewed through 2 B+ wires at the fuse block, 2 wires coming from the TAC module located on the firewall, and a ground wire that ran to the ECM I believe. Upon further inspection of the fuse block and wires, the underside of the block was badly corroded outside and in and smelled of burned wiring. Wonderful... The TAC module also emitted a burned wire smell when I tapped on it. I theorized that this rat, spawned from satan himself, had chewed these wires causing a short and likely frying some modules when I moved some wires specifically to **** me off and lead me to an even stronger hatred for rats. SO, I proceeded to replace the TAC module, the accelerator pedal sensor, Fuse block, repaired/replaced all broken/chewed wires, replaced the ground strap and added an additional ground strap from the firewall to the block cause why not. Relocated the TPS/Actuator ground to a more convenient and clean location, cleaned the MAF sensor with some CRC cleaner and replaced the instrument cluster because it had lost the back lighting for PRND321 selection and had something going on with other lights which was, coincidentally happening before the DEP message. Checked the small fuse block by the drivers door, all wires I could get to behind the knee bolster and instrument cluster, wiring in the steering column and the ignition switch and pigtails.
Now after all of that, you would think it would be done right? You would be wrong... Upon initial start up, the truck ran great and throttle response was perfect. I was skeptical, so I took it for a test drive. Drove great. Parked it, shut it off and started it again a couple of times, then it threw the DEP message again with no accelerator response and codes p1518 (TAC to ECM signal circuit, not finding much information on this code) and p0220 (Throttle/Pedal Position Sensor/Switch "A" Circuit Malfunction) I cleared codes, and it fired right up, drove great again. stopped again, shut it off and started it back up no problem and drove home. Got to my driveway and shut it off, started it back up and it gave the DEP message again. I have double checked all grounds, wires and everything I can think of. It seems to be random, follows no pattern. Sometimes I can start and run it 20 times in a row with no DEP or codes before they set again. Sometimes it happens again and again, always the same 2 codes... P1518 and P0220. And every time they set, if I clear them the truck starts and runs great until it is shut off and restarted. My next step, I guess, is going to be taking it to the stealership and have them test the ECM and see if it is functioning properly. This truck is driving me crazy and I have too many other projects stacking up and a list of other client vehicles to get to. I have gotten a great deal of information from this forum site and am hoping someone can give me an idea what to do next aside of replacing the ECM. Help?
