Throttle Position Sensor
 

Hi guys, my daily driver is parked and I'm at my wits end. 2002, 2500, 5.9L stock, 4x4, 6sp. While driving home I lost throttle control, engine only idled, occasionally it will gain a little RPM. Through code P0122 for throttle position sensor. Purchased a new TPS from NAPA and installed. Truck ran great for 5-10 minutes and on the test drive TPS went away and back to idle only. Tested TPS back to the ECM all wires are good. TPS tests good with 5v with key on engine off. Once engine is started TPS losses voltage and stops working. Thinking it may be voltage related I bought new batteries. Then went through every ground on the truck, taking the ground off, cleaning and reattaching (the grounds looked good before taking them off). Still no change. So then I figured it must be the ECM. New ECM and no change. Then I thought I probably got a bad part from NAPA so I ordered another TPS from Geno's. Geno's TPS ran good for 2-3 minutes and then went away. With the Geno's TPS and my old ECM I can get the code to clear and start the truck (starting was never an issue). After starting everything is fine at idle, no codes. The voltage at the dash display comes up to 14v until the something cycles on for about 5 seconds then cycles off for about 15 seconds. I am pretty sure this is the grid heater. When the heater cycles on, the voltage drops to approx 11v. If I give the truck throttle when the voltage is down, I lose throttle and P0122 comes up. If I wait for the voltage to return to 14ish I have normal throttle. I noticed the lights have dimmed when the heater turns on since I bought the truck 6 years ago, so I did not think anything of it. Is it normal for the voltage to drop that far? Is it possible that the grid heater is going bad and it is drawing too much and the TPS is just the first thing to lose signal? How do I test the grid heater? Mostly Whiskey Tango Foxtrot!!! Thanks for any help or advice you can give, Pete.

Possible electrical noise from alt or fuel pump. Try disconnecting field wire at alt. See if code returns. If it does then try disconnecting fuel pump, measure the AC noise on battery voltage to ECM, is the voltage above 25mVrms? (Possible electrical noise from the Transfer pump). Was code stored in PCM or ECM?

Diagnostics for code p0122

Thanks BigIron. Ill check for voltage noise. Ill double check but I'm pretty sure all of the diagnostics in the PDF have been done. And I forgot to mention a new alternator was installed with no change.

PCM
Cav circuit function
1 - -
2 f18 18lg/bk fused ignition switch output (run-start)
3 - -
4 k4 18bk/lb sensor ground
5 - -
6 t41 18bk/wt (a/t) park/neutral position switch sense
7 - -
8 k24 18gy/bk crankshaft position sensor signal
9 - -
10 - -
11 - -
12 - -
13 - -
14 - -
15 - -
16 - -
17 - -
18 - -
19 - -
20 - -
21 - -
22 a14 14rd/wt fused b(+)
23 k22 18or/db throttle position sensor signal
24 - -
25 - -
26 - -
27 - -
28 - -
29 - -
30 - -
31 z12 14bk/tn ground
32 z12 14bk/tn ground


ECM

ENGINE CONTROL MODULE (DIESEL) - 50 WAY CAV CIRCUIT FUNCTION
1 H104 18BR/OR IDLE VALIDATION SWITCH NO. 1
2 K244 20YL/DB CUMMINS BUS (+)
3 K6 18VT/WT 5V SUPPLY
4 K14 18BK/DB SENSOR GROUND
5 F18 18LG/BK FUSED IGNITION SWITCH OUTPUT (RUN-START)
6 G60 18GY/BK ENGINE OIL PRESSURE SENSOR SIGNAL
7 K21 18BK/RD INTAKE AIR TEMPERATURE SENSOR SIGNAL
8 G12 18GY/RD MANIFOLD ABSOLUTE PRESSURE SENSOR SIGNAL
9 - -
10 K7 18OR 5V SUPPLY
11 K104 18BK/LB SENSOR GROUND
12 K246 20YL/DG CUMMINS BUS (-)
13 K242 20WT DATA LINK (+) FUEL INJECTION PUMP
14 K2 18TN/BK ENGINE COOLANT TEMPERATURE SENSOR SIGNAL
15 K135 18YL/WT TRANSFER PUMP SUPPLY
16 H105 18LG/DB IDLE VALIDATION SWITCH NO. 2
17 K124 18GY CAMSHAFT POSITION SENSOR SIGNAL
18 K48 18DG FUEL INJECTION PUMP SYNC SIGNAL
19 - -
20 - -
21 K1 18DG/RD WATER IN FUEL SENSOR SIGNAL
22 V37 18RD/LG SPEED CONTROL SWITCH SIGNAL
23 K240 20BK DATA LINK (-) FUEL INJECTOR PUMP
24 V32 18YL/RD BRAKE SWITCH SENSE
25 H102 18LB/BK ACCELERATOR PEDAL POSITION SENSOR SIGNAL
26 G113 18OR PTO SWITCH SENSE
27 - -
28 K22 18OR/DB ACCELERATOR PEDAL POSITION SENSOR SIGNAL
29 S21 18YL/BK AIR INTAKE HEATER RELAY NO. 1
30 Z12 18BK/TN GROUND
31 H101 18DB/WT ACCELERATOR PEDAL POSITION SENSOR SUPPLY
32 H103 18BK/YL ACCELERATOR PEDAL POSITION SENSOR GROUND
33 K45 18LB/RD FUEL SHUT-OFF SIGNAL
34 K44 18VT/OR LOW IDLE SELECT
35 K135 18YL/WT TRANSFER PUMP SUPPLY
36 K131 18BR/WT FUEL INJECTOR PUMP RELAY CONTROL
37 G85 18OR/BK WAIT-TO-START WARNING INDICATOR DRIVER
38 D21 18PK/DB SCI TRANSMIT
39 D20 18DG SCI RECEIVE
40 D2 18WT/BK CCD BUS (-)
41 D1 18VT/BR CCD BUS (+)
42 - -
43 G7 18WT/OR VEHICLE SPEED SENSOR SIGNAL
44 K243 20OR/BR DATA LINK SHIELD FUEL INJECTOR PUMP
45 K24 18GY/BK CRANKSHAFT POSITION SENSOR SIGNAL
46 - -
47 S22 18OR/BK AIR INTAKE HEATER RELAY CONTROL NO. 2
48 A14 18RD/WT FUSED B(+)
49 Z12 18BK/TN GROUND
50 A14 18RD/WT FUSED B(+)

You can try disconnecting the grounds on the heater relays. If code is only setting when heaters come on. They ground same location as the ECM ground according to wiring diagram at location S168 and S109. Make sure you have a good ground connection there measure resistance from relay to ground, ecm to ground pin 49 and 30 at the ecm

S168 (Diesel) Engine Harness, Near T/O to Engine Coolant Temoerature Sensor

S109 Battery Harness, In T/O for Engine and Transmission Ground

I suggest you also disconnect your batteries then take all 3 plugs for the PCM that are located on the firewall passenger side and use contact cleaner. Soak them and plug/unplug them a dozen times, spray a little between every 3-4 plug ins and then blow dry with air and plug back in, hook up your batteries and see if that helps. I lost many items and OD once and that is all I had to do to get everything back working properly.
Worth a try.

Problem ended up being a bad Cummins computer. It is located on the drivers side of the engine, behind the fuel filter. Replaced it Feb. 2013. Been running great ever since.

where did u get ur cummin comouter and how much was it? (If u dont mind me asking)

PCM is on the fire wall ECM is behind the fuel filter

This is a very old thread so you may want to post your question as a new thread. You will get some quick responses from the experts here :) My bad, I see that the post that you are responding to is recent, you can also pm him...Mark