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spankyjr1, Journeyman
Category: Medium and Heavy Trucks
Satisfied Customers: 2662
Experience:  Journeyman TechnicianWorked on small to large engines for 30 yearsGas,LP,Diesel
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Hi there I have an Allison HD 3066 fitted to a 2004 P93 Scania

Customer Question

Hi there
I have an Allison HD 3066 fitted to a 2004 P93 Scania The fault codes are as follows.
D1 5587 D2 3255 D3 5597 D4 2312 D5 3233. The Symptoms are when reverse is selected it selects for 2 seconds and then goes into a safe limp mode which is 5th gear. If you drive forward the truck will drive normally up into 6th gear but after about 10 miles will also go back into limp mode 5th gear. the fault codes relate to C3 pressure switchs is this a switch or pressure fault. Any help?
Submitted: 4 years ago.
Category: Medium and Heavy Trucks
Expert:  spankyjr1 replied 4 years ago.

Hi Jason and welcome

This is most likely a electrical problem not a pressure problem.

1. Disconnect the connectors at the ECU and the transmission. Check the C3 switch circuit for opens,shorts to other wires, shorts-to-ground, or shorts-to-battery.
If wiring problems are found, isolate and repair.
The C3 pressure switch closes at 206.8 ± 48 kPa (30 ± 7 psi).
Resistance should be
2 Ohms maximum when the switch is closed and 20,000 – infinity (overlimit) Ohms when the switch is open.
2. If problems are not found in the external harness, drain the fluid, remove the control module, and
check the internal harness for opens, shorts between wires, or shorts-to-ground (refer to the proper transmission Service Manual).
If wiring problems are found, isolate and repair (see Appendix E,
Paragraph 1–9).
3. If no wiring problems are found, replace the C3 pressure switch (refer to transmission Service Manual).
4. If the problem recurs, use spare wires for the C3 pressure switch circuit.
5. If the problem recurs again, replace the internal harness.
6. If the condition persists, replace the ECU. If replacing the ECU corrects the problem, reinstall the original (bad) ECU to confirm that the problem is in the ECU.
If the original ECU now works,
inspect the ECU connectors for any corrosion or damage which may cause an intermittentcondition.
If the original problem recurs, reinstall the replacement ECU.,d.aWc

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