Where does PCM/ECM sensor ground wire attach?
#1
03-09-2015, 09:20 PM
Where does PCM/ECM sensor ground wire attach?
The black ECM plug has a black with light blue ground wire in position no. 4
that provides a ground for the engine coolant temperature sensor, the intake temperature sensor, and the manifold absolute pressure sensor. I have had mice chewing on wires and have repaired them, but now I have a trouble sensor P0117 (engine coolant temperature sensor low input) which makes the engine hard to start and die intermittently (dangerously so at intersections). Does anyone know where this black with light blue ground wire ends up after it leaves the ECM? Does it ground on the firewall, chassis, motor? I can't figure out where its end grounding point is. I want to check the ground before I change the sensor because I have read some posts where changing the sensor did not solve the problem. Not only that, the sensor looks like it is underneath the A/C compressor of all places! This is a 1996 Dodge Dakota 3.9 standard transmission 4 X 4 purchased new from the dealer by my Dad with 260,000 mile now and counting. Thank you.
Update: I think I asked the wrong question above. According to the factory wiring diagram the black plug of the ECM has two black and tan ground wires at positions #31 and #32. If the ground for the coolant sensor goes both in and out of the ECM, then the black with light blue wire might internally pass through a circuit in the ECM itself and then ground outside of the ECM (by way of one of the two ground wires at #31 or #32). I will check it out.
Update: Wires #31 and #32 ground on top of the alternator bracket with one larger gauge black/tan wire.
Diagnostic update:
Pulled radiator hoses, radiator, shroud, and moved A/C compressor to inspect ECT sensor. Checked continuity of tan/blk (ECT sensor signal) and blk/lt. blue (sensor ground via ECM) wires from sensor plug to ECM and both wires checked out OK. Checked voltage from tan/blk wire coming from ECM with ignition on and read 5.2 volts which is OK. Cleared 0117 code with old ECT sensor still in place and 0117 code repeated immediately. Unplugged sensor plug, cleared 0117 code and received 0118 code, which is to be expected. Plugged new Standard Brand ECT sensor (#TX71) into plug (without screwing into motor), cleared 0117 code, and code stayed away. Based on these tests, it would appear the old ECT sensor is at fault. New sensor reads 7.65 Ohms (1000 range) out of the box and 6.8 Ohms (1000 range) after sitting in the sun for about an hour. Will return Duralast ECT sensor I bought by mistake when I forgot I had bought the Standard Brand ECT sensor over a year ago and never used it. By the way, the Standard Brand sensor has a red sealant on the threads and the Duralast sensor had bare threads. In my opinion, being the fact the ECT sensor is two wire, it does not have to ground itself by the threads that go into the intake manifold.
that provides a ground for the engine coolant temperature sensor, the intake temperature sensor, and the manifold absolute pressure sensor. I have had mice chewing on wires and have repaired them, but now I have a trouble sensor P0117 (engine coolant temperature sensor low input) which makes the engine hard to start and die intermittently (dangerously so at intersections). Does anyone know where this black with light blue ground wire ends up after it leaves the ECM? Does it ground on the firewall, chassis, motor? I can't figure out where its end grounding point is. I want to check the ground before I change the sensor because I have read some posts where changing the sensor did not solve the problem. Not only that, the sensor looks like it is underneath the A/C compressor of all places! This is a 1996 Dodge Dakota 3.9 standard transmission 4 X 4 purchased new from the dealer by my Dad with 260,000 mile now and counting. Thank you.
Update: I think I asked the wrong question above. According to the factory wiring diagram the black plug of the ECM has two black and tan ground wires at positions #31 and #32. If the ground for the coolant sensor goes both in and out of the ECM, then the black with light blue wire might internally pass through a circuit in the ECM itself and then ground outside of the ECM (by way of one of the two ground wires at #31 or #32). I will check it out.
Update: Wires #31 and #32 ground on top of the alternator bracket with one larger gauge black/tan wire.
Diagnostic update:
Pulled radiator hoses, radiator, shroud, and moved A/C compressor to inspect ECT sensor. Checked continuity of tan/blk (ECT sensor signal) and blk/lt. blue (sensor ground via ECM) wires from sensor plug to ECM and both wires checked out OK. Checked voltage from tan/blk wire coming from ECM with ignition on and read 5.2 volts which is OK. Cleared 0117 code with old ECT sensor still in place and 0117 code repeated immediately. Unplugged sensor plug, cleared 0117 code and received 0118 code, which is to be expected. Plugged new Standard Brand ECT sensor (#TX71) into plug (without screwing into motor), cleared 0117 code, and code stayed away. Based on these tests, it would appear the old ECT sensor is at fault. New sensor reads 7.65 Ohms (1000 range) out of the box and 6.8 Ohms (1000 range) after sitting in the sun for about an hour. Will return Duralast ECT sensor I bought by mistake when I forgot I had bought the Standard Brand ECT sensor over a year ago and never used it. By the way, the Standard Brand sensor has a red sealant on the threads and the Duralast sensor had bare threads. In my opinion, being the fact the ECT sensor is two wire, it does not have to ground itself by the threads that go into the intake manifold.
Last edited by Dibbons; 03-11-2015 at 05:18 PM. Reason: wrong question