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This summer the truck developed an issue - when I would give it medium / heavy throttle, the check engine light would come on. If I left off the throttle a bit, it would go away. At this time I was hauling through the mountains back and forth in a heatwave. I always run forscan while I drive, but there was nothing out of the ordinary showing, so I just feathered the throttle to keep the check engine light from coming on.
Fast forwards a month or two ahead, and the truck has gotten worse. At startup it will not set a check engine light which eventually goes away after a minute or two of idling. When driving, the check engine light comes on with light to medium throttle, and will disappear if I let off the throttle and coast, or only give it a tiny bit of throttle. As far as I can tell, it still drives perfectly fine.
Here are the codes I have pulled:
U1027 - no rpm data (rpm shows fine on dash and in forscan)
U1262 - communication bus failure (all modules showing as active and working in forscan though)
P0221 - throttle switch B circuit performance (throttle works fine)
P1316 - idm codes (did buzz test only shows P1298)
P1298 - idm failed (truck drives fine though)
The work I have done so far is to check / clean the connectors at the IDM, PCM, GEM, 42 pin connector, and all engine sensors. I've continuity checked most of the engine harness back to the 42 pin connector. Checked injector resistances. Under valve harness is new. Alternator is only a year old and outputting 13.9v (although I have not checked any of the AC output on it yes). Checked in cab grounds (both sides). Visually checked all the wiring under the dash for obvious chafing or breaks. Cleaned and checked 42 pin connector for any burns or chafing at crossing valve cover. Injectors all buzz strong. Have verified all injectors are passing oil properly. Fuel pressure is solid at 55 or so psi.
While driving, all values monitored on forscan show fine - I monitor speed, RPM, ICP, IPR, fuel pulse width, voltages (both battery and 5v reference), map, ebp, oil temp, trans temp, etc etc. No issues in any of the monitored parameters.
I'm at a loss here - and considering ordering a new IDM. The IDM I have is a remanufactured one, and I have read that they can throw a code for P1298 - but it only started throwing this code recently, so my thinking is that something must have changed.
The only thing that I did different this summer was a bunch of heavy hauling through mountain passes in a heatwave - but I cannot find any component that was damaged due to heat. My cooling system is working fine, and although I did hit some high oil temps during the summer, the cooling fan came on quickly and dropped the temps back to where they needed to be.
Do you have a log you could post of all those PIDs when the SES light comes on? Would like to look for gliches in the data.
The wiring is suspect on these old trucks now. You might have an intermittent connection or two between the PCM and IDM, or between the IDM and the injectors. It might be worth checking with a meter. Procedure attached.
If the wiring checks out, your symptoms, and the reman IDM (where did you source it?), would point me toward a replacement IDM - though I would send that one in to dieseltechchatt and have them repair it, after giving them a call to discuss. Forum members here have had good experience and support from this company.
What prompted you to replace the IDM the first time? How did you discover it needed to be changed out?
What tuner/chip are you running? This thread shows a guy getting P1298 only when the chip is in. He just ignored and kept running it. If your truck is running ok, you could just drive it.
Do you have a log you could post of all those PIDs when the SES light comes on? Would like to look for gliches in the data.
The wiring is suspect on these old trucks now. You might have an intermittent connection or two between the PCM and IDM, or between the IDM and the injectors. It might be worth checking with a meter. Procedure attached.
If the wiring checks out, your symptoms, and the reman IDM (where did you source it?), would point me toward a replacement IDM - though I would send that one in to dieseltechchatt and have them repair it, after giving them a call to discuss. Forum members here have had good experience and support from this company.
What prompted you to replace the IDM the first time? How did you discover it needed to be changed out?
It's a GB remanufacturing IDM in there with the 120V mod according to the label on the IDM - came with the truck when I bought it (2 years ago). I've gone through that GB bulletin test (in fact have read nearly every post related to my types of errors on this site and other powerstroke sites). I will do a test on the PCM connector. My suspicion is that I have an intermitted ground or short that comes on during acceleration. The check engine light only used to come on during medium to high acceleration, and now its low to medium acceleration. This makes me think that a wire is shorting or a ground is failing "easier" than before. I've built a load tester using a 12v headlamp to test wires, as so far it was just continuity test and resistance test.
What tuner/chip are you running? This thread shows a guy getting P1298 only when the chip is in. He just ignored and kept running it. If your truck is running ok, you could just drive it.
I have a php hydra, but I have verified it still acts the same with the chip in the pcm, chip set to stock, or chip removed. I've had this setup for nearly 2 years and it has not caused any issues until now. The truck runs OK, but it is throwing these error codes, which I believe are all false codes.
You've done your homework and checked much to this point. It would be nice to get to the bottom of this and understand the cause, but at least it's not stranding you. Would it be worth pulling the IDM and open it up, get eyes on the components, and see if reflowing the solder on a few that look questionable is warranted?
That is on my list to do - so far I have removed the IDM to visually inspect it. The connector is clean, no corrosion seen. The outside of the unit looks in good shape as well, no visible water stains. The PCM looks equally clean.
I've seen some youtube videos on what they do to "rebuild" these, and what components are replaced during rebuilds, but I am not ready to open it up quite yet, in case I ruin it, as it's my daily driver. If I had a second IDM on hand (in case I ruin the first one) I would not hesitate to open it up. I did open up the GEM module and did a closeup check on the components and shine a bright light through the circuit board which would show burnt areas (chasing down the U1262 code), but I do believe the U1262 has to do with PCM / IDM communication. As far as I can tell, the IDM / PCM only share 4 connections (IDM#2-PCM#91 sensor signal return,IDM#16-PCM96 cylinder identification signal output, IDM#17-PCM#95 fuel delivery command signal, IDM#4-PCM#48 diesel electronic driver unit.)
Perhaps if the sensor signal return between the two is problematic, it could account for some sensor issues which is throwing codes and the failure to communicate between the IDM / PCM - so I will look into that tomorrow, but I will continuity check and load test all 4 of these wires between the IDM / PCM plug.
Do you have a log you could post of all those PIDs when the SES light comes on? Would like to look for gliches in the data.
Here is a snapshot just going down my driveway, about a 4 minute drive in total. This is with the php tuner. Have to run to town, will put it into stock mode tomorrow and record a WOT run up to highway speeds.
Okay here are some snapshots from todays test. No tuner. The first one is a 0-100kmh acceleration at 1/2 - 3/4 throttle, then driving at highway speeds normally.
The second one is driving at highway speeds, and doing 3 WOT pulls. Only thing I notice is I probably have a boost leak - boost only getting up to 13psi at WOT pulls. When I have my tuner installed I can over boost at WOT. I cannot see any indication or reason why the check engine light is coming on or off - it really seems to me, as I drive it, that when I give it throttle, it will come on, and if I lay off the throttle and allow it to coast, or just give it much less throttle, barely enough to keep it going, it will go away.
Do these trucks have a redundant circuit for the throttle pedal sensor? I would assume they do. The ones I’m slightly familiar with use both channels as a redundancy safety feature. Maybe one of the 2 (“B”) has an issue that’s popping the SES? Now getting worse and showing at more throttle positions?
Just something to chew on.
BWST, is there a way to monitor both channels in FORScan?
Do these trucks have a redundant circuit for the throttle pedal sensor? I would assume they do. The ones I’m slightly familiar with use both channels as a redundancy safety feature. Maybe one of the 2 (“B”) has an issue that’s popping the SES? Now getting worse and showing at more throttle positions?
Just something to chew on.
BWST, is there a way to monitor both channels in FORScan?
There are 5 wires from the throttle pedal position sensor :
1. Brown / White to PCM#90 - 5v reference. Have verified it has 5v at key on. Have also verified it connects back to PCM#90 without a short by load testing.
2. Gray / White to PCM#89 - Acceleration position sensor. I've tested this in forscan by sweeping with KOEO - it seems to work fine. No abnormal spikes in values.
3. Yellow / White to PCM#24 - Throttle position sensor. I did get a throttle position sensor error twice, in conjunction with loss of throttle that came back after a few seconds.
4. Red / Yellow fuse #45 hot at start / run position. Fuse #45 has power.
5. Red / Light Green to PCM#10 - Idle Validation. Idle on forscan shows "idle / off idle" properly - I believe this is all it does.
I have another throttle pedal with sensor on order from rockauto since I did get the throttle position sensor error 2 times in the last month.
I've tried driving with forscan on in the errors tab and re-reading the codes when the check engine light comes on, hoping it would show what exactly is throwing the code - but whatever it is, it is either one of the previously set codes, or something that is not coming up. I've reset all the codes and verified no codes stores and started driving, and upon the check engine light illumination have refreshed the codes, which shows only a P1316. Stopping and doing a buzz test then brings up P1298. As per my first post, there seems to be no issues with the IDM though.
Driving along some more, eventually I get all the same codes that show up - U1027 - no rpm data and U1262 - communication bus failure.
You can monitor these in forscan - IVS (idle validation switch) and the other two related to throttle are throttle position (which I believe has 3 modes) and accelerator position (which I believe just outputs in G force or something). I will add these and do another run this week to see if there is any correlation.
Do these trucks have a redundant circuit for the throttle pedal sensor? I would assume they do. The ones I’m slightly familiar with use both channels as a redundancy safety feature. Maybe one of the 2 (“B”) has an issue that’s popping the SES? Now getting worse and showing at more throttle positions?
Just something to chew on.
BWST, is there a way to monitor both channels in FORScan?
I did 2 runs, one accelerate to highway speed, and another at highway speed going WOT. Pedal position voltage and idle validation both show fine in both runs. I also tracked "throttle position rate" for which I cannot find any description for, except it measures in "G forces", and will fluctuate between 0 - 1600 G's. I've searched for this online, and the only descriptions I've found of it are also people that have a similarly behaving throttle position rate that jumps erratically. Someone says that it's just a value the PCM uses to figure out torque ratings, but I'm still not 100% sure what it is.
Are you still getting the SES light and IDM codes P1316 and P1298? P1316 is the only one that would set the SES light that I can see. Again, if no driveability issues, I'd keep running it, or get eyes on the IDM circuitry.
Can you attach the raw data in CSV format? I don't do well with screenshots - hard to get the resolution needed and to compare drives/parameters to each other. I'm not familiar with some of the PIDs you have selected, and don't know if they are providing supported data for the 7.3 platform, but thank you for trying them - it's interesting to see.
Are you still getting the SES light and IDM codes P1316 and P1298? P1316 is the only one that would set the SES light that I can see. Again, if no driveability issues, I'd keep running it, or get eyes on the IDM circuitry.
Can you attach the raw data in CSV format? I don't do well with screenshots - hard to get the resolution needed and to compare drives/parameters to each other. I'm not familiar with some of the PIDs you have selected, and don't know if they are providing supported data for the 7.3 platform, but thank you for trying them - it's interesting to see.
Yes, the SES light is the MIL light (Malfunction Indication Light) in the charts. It basically turns on at anything past low throttle, and stays on until I return to low throttle, even though there seems to be no issues with the throttle pedal or any of the other sensors. No drivability issues, but I will open up the IDM once my latest amazon orders arrives. CSV's attached.
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