tps circuit problem

[hamold1]

Trans shifts hard 1-2 slightly hard 2-3 no overdrive...has code 18 something will have to get the right # code means tps circuit low voltage...dealer installed new gm tps sensor was fine for a month now problem back again...could it be ecm..or maybe bad wiring or connection??? any common problems out there??? 1993 gmc k2500 4l80e 6.5td

[Robyn]

Hi

One of the most common issues with these newer vehicles with all the miriad electronics is a sensitivity to voltage and grounding issues.

Be sure the grounds at the rear of the intake manifold on the RH side of the truck are clean, tight and in good order.
There are usually two and sometimes more wires from the harness that connect a bolt on the rear RH side of the manifold.

The other issue is the battery grounds, both at the battery itself and the point at which they connect to the engine block.

The positive cable too can cause an issue.

If the cables have a lot of time and miles on them the only real good way to be sure there is no issues is to replace them.

The side terminal cables corode under the red end jackets and into the core of the cable where it cant be seen.

Many times the battery that receives the charge from the alternator (Can be right or left depending on the year of the vehicle) will have a good positive connection but the ground will be bad.

On the early trucks (92-94) the alternator charges the LH battery but the power to the chassis is fed off the RH battery via a #4 cable that runs under the engine and up to the Junction on the firewall at the RH upper side.
The later trucks (95 on) feed the batteries a bit different depending on the exact year but the power is fed to a large distribution box on the LH inner fender.

If the power feed becomes poor the ECM will do all sorts of crazy stuff.

You should see 14-14.7 volts at the batteries and at the main positive bus in the distribution box when the engine is running.

If you dont see this, find out why and fix it.

An alternator that has a diode that is failing and causing alternating current in the system can drive the ECM and other components "NUTZ"
resulting in various drivability issues.

The issue can possibly be a tranny issue as in a poor connection at the main harness connector at the transmission.

Remove the plugs at the tranny and spray the connections with contact cleaner and reinstall and test.

These sort of issues can be a real PITA to diagnose.
The systems are quite complex and have a lot of circuits that use grounds that interconnect and ultimately fasten to the chassis.

One poor ground connection and all sorts of things can happen.

Now
The 93 trucks have a very simple ECM compared to the later trucks. The ECM controls the tranny and a few other things but is not nearly as complex as the 94 and later rigs.

If all the voltage and ground checks turn up nothing I would start to get suspect of the ECM/PCM

Poor connections can happen due to corrosion and moisture entry into connectors.
The weather pack and metripack connectors are fairly good but can over time and exposure to the elements have troubles.

If the installation of the new TPS rectified the issue for a while it very well may be the connector at the TPS.
Try unhooking the TPS and spraying the connector with contact cleaner and then hooking it back up.

If this resolves the issue you have your Gremlin at hand.

If you live in a wet area and especially one that sees salt used on the roads connection issues can be a problem.

Give it a go and let us know what shakes out.

Best

Robyn

[More Power]

Unplug the TPS (at the TPS), then measure the voltage between the black and gray wires terminals with the ignition key in the RUN position. You should see almost exactly 5.0 vdc. If you don't, you'll need to measure the voltage at the appropriate pinout at the TCM to eliminate a wiring problem. The TCM generates the regulated 5.0 vdc.

If the 5.0 vdc is OK, reconnect the TPS connector, then use a pair of straight pins to pierce the black and blue wires close to the TPS. Piercing the wires with straight pins allows you to use your multimeter to measure the voltage on those wires. Gotta be careful not to allow the pins to short to each other or to an engine component. Your multimeter should see a smooth varying voltage between about 0.5 vdc at idle and 4.5 vdc at full pedal. Of course, a Tech I scan tool can be used to measure the TPS response as a percent of throttle angle.

Jim

[DIESEL5]

hey there i am new too the diesel page and have found alot of interesting info My 93 6.5 is giving me some headache its very hard shifting from first to second and no overdrive I have checked the grounds and all seem to be good Ijust did a head job on it with new injection pump and new injectors and cant figure out this tranny problem any help would be greatly appreciated its driving me nutz!!!!!!!!

[DIESEL5]

can anybody tell me exactly what the blue,Gray,Black wire voltage readings should be or which one is ground i assume the black one is ground and blue reads five volts what about the grey wire

[More Power]

Black - ground (at least for the TPS circuit - may not be a vehicle/chassis ground).

Gray - this is the 5 vdc regulated reference voltage generated by the TCM.

Blue - this is the variable output of the TPS. Should about 0.5 vdc at idle and 4.5 vdc at full pedal.

Jim

[hamold1]

Took it back to the dealer and the diesel tech checked everything out. He readjusted tps and it has not acted up since...????